Here's my understanding of the bow stance. In practice and training the leg extends and becomes straight as kung fu drives power by pushing into the punch. In order to get maximum power, you want to straighten that back leg so that the leg is pushing all the way through.You know Kung Fu, you should know the worst stand you can have is in the picture, straight legs and spread far apart. For wide stance, you need to bend the knee a little to get the bounce,
In application the back leg is not straight like in training. It doesn't go completely straight like in training It's straight -ish for a short period of time. Literally less than a second. By the time your punch lands your fist and your leg are returning back to position. It's not the long extended straight leg that you see in training but it does get fairly straight sometimes, just not completely straight.
Here is a good example of what I'm talking about. If you drive punching power by pushing into your punch then this is about as straight as it's going to get before the stance transitions into something else. This is similar to the punch that I first showed you when you first joined here.
Boxer's and MMA fighters sometime are too front heavy because of how they drive power. When that happens their rear foot comes off the ground. The risk of that rear foot coming up is that you are now standing on one leg. You can get away with it in boxing because there is no kicking. But if kicking is involved then standing on that front let with your right leg off the ground can be dangerous.
Some fighter do it because they are transitioning in footwork placement, sort of sneaking a step while punching. Other are literally falling forward and look as such as you see them stumble out of their punch.
Boxer typically take the wider stance, it's more stable for launching your hardest punches. High stances are more mobile but they are also less stable. If you take a high stance against a grappler (bjj, judo, or any style of wrestling), then you put yourself at a much greater risk of being put on the ground. Standing tall against them would almost be like taking the newbie student down at the gym. Stance high will vary depending on what you are facing. I start off a mid level stance because at that point it's faster for me to raise or lower my stance as needed.OR standing up straight with feet close together like boxing so you can easily hop around.