Bending the arm that way is how i always train that strike in the heavy bag at head level, works fine so that I can hit with seiken. I would now strike with the smaller knuckles on a head without good gloves, so even if we dont strike to head in sparring, I train these full force on the bag, I and I always try to envision the surface I am hitting. Which is nothing like a heavy bag. I sometimes do it with less power on a beam with soft padding, just to feel the feedback. If it feels evenly distributed I conclude its good, if the pain is sticking out somewhere, wrist, elbow etc.. then something with the linkage or alignment is likely wrong. Hitting hard with the weak knuckles feels not great.