Thanks for your elaborated response, and confirming it from your experience!
Okay I'm back haha. My main background is Kyokushinkai, and our sanchin dachi was as you described, and all kihon were performed from this stance too (except kicks).
I also never really got an explanation why it is so much more extreme than other styles' sanchin dachi. I feel like it still is built upon the ideas of its origins, sinking your weight, protecting the groin, and creating almost an inward spiral effect into the ground and optimising stability.
This is exactly how i think of ti as well, and these principles are I think quite sufficient, and a sanchin-like stance appaears naturally. Specific optimal angles etc, are likely completely individual? or so I like to think. Many factors, hip rotation, and may also feet/ankel flexibility and other things would matter.
My theory is, because it seems pretty all basics/kihon in Kyokushin is really exaggerated that this was simply an outgrowth of that. Sosai seemed to like the bigger movements to develop full range strength. Everything seemed bigger, grander and big power-focused.
I wasn't a big fan of the sanchin dachi and it hurt my knees a bit haha.
Our sanchin dachi in Goju is different, back foot facing straight ahead, the front foot's heel in line with the back foot's toes (this part is the same), but we lean more towards the front foot being more natural and only slightly turned in. Also another thing is we actually almost fully straighten the back leg. Not locked but straight rather than with a bend. We also tuck the pelvis to a natural position to align everything. We really focus on sinking our weight, which initially was tricky for me with the straightened back leg (as you can easily raise your centre through pushing up through that back leg straightening action). But I found straightening the back leg in conjunction with the posterior pelvic tucking motion assisted in sinking the weight.
So Sosai coming from both shotokan, and goju ryu background, decided to change the sanchin from both. This can't be for no reason.
And I've always said it's not so much about the front foot angle but it being about the slight internal hip rotation. You can then drop/bend the knees and the knees should come together (NOT cave in but move in towards each other as they move forwards) to protect the groin further.
But I'm always interested in everyone's thoughts on sanchin dachi. I think as long as it adheres to those principles of sinking the weight, feet flattening through the ground (as opposed to gripping which can actually being the feet up into a higher contracted position thus losing connection with the ground), postural alignment, and developing rootedness, being grounded and stable, all is good
This is in line with my thinking as well, thanks for confirming my thinking!
In class I get what I as a beginner feel is superficial comments about the angles beeing off. But as a humble beginner, it is not on me to question the senpai, in particular not in class. But I can not stop thinking that there is something here that isn't entirely right. Unless I get an explanation from senpai, why this feeling is misguided(if it is), it's going to stay. At end of the day, no matter how much I respect our instructors, if it feels wrong in my body in terms of poor stability etc, then something can't possibly be right.
Also I have from physio visits, documented poor internal hip rotation, but at the same time I have outstanding external hip rotation (much better than most). So my overall rotation range is normal, the offset is just biased towards external. I think this is the explanation. This is why the standard angles just seems impossible for me.
For the same reason, I like the valeri style heel kick much more than the normal mawashi geri(I have to turn more than others to get the optimal angle). I have flexibility to pull this kick off as high as armpit level. Had I just been for flexible it would morph int on axe kick, but I lack flexibility in the other way to do that.
But OTOH, don't we ALL have our biases? So why not teaching constructing principles instead of angles from pictures?
In terms of you mentioning you feel highly unstable in it, is your weight centred 50/50 between feet? Do you feel like you are sinking your weight down rather than being raised up? Maybe experiment also with alternating between inward tension (squeezing inwards with adductors without caving knees in) and outward tension (pressing down and
out using glutes) through the legs/feet. See what feels better and more stable for you. And then try neither. But sinking weight and feeling like you're simultaneously being rooted deeply into the ground whilst simultaneously being pulled upwards from a string attached to the top of your head is key
I can experiment a bit with what you suggest, but when I feel unstable it is only when I focus on the look, more than the feel! Ie if push my interior hip rotation to it's limits, and my feets to the limit, to get "as close to the ideal angles as I can" in absurdum, then what happens is that I loose that feeling of sinking in deep, and I feel like I am pivoting on a pin in terms of balance. So this is the best I can do to get "as close as possible", but I FEEL that this is wrong, and in contradiction with what I THINK are the constructing principles of this stance.
If I OTOH, don't care about the exact angles, jsut lower my gravity and angle the feet by internal rotation of both hips and try to feel how my body pushes the "pyramid" into the ground, and I can "bounce a little bit up and down" and feel the tension, than I feel very stable, I use this stance often when holding mitts, to be able to better resist not foward strikes byut also angles attackes without moving stance alot. When I then look down on my feet, I am closer to sanchin of shotokan.
My hypothesis is that this is likely the "sanchin dachi" for ME that is most faithful to the presume constructing principles, even though it is not quite "as close to the looks" of the ideal angles.