Personally, I usually practice palm forward. At first, I can put my hands flat on my shoulders and raise my hands over my shoulders. This is an advanced method of this movement, which can stimulate my muscles better.

As for whether the middle bundle of deltoid muscle should be stimulated with a small number of groups, you can try a little less or a little more to see which muscle is sore after training. Everyone's situation is different, and it is difficult to generalize. Just find the one that suits you best. You can also consult a professional coach in the gym and let him see how to practice according to your personal situation.

I'm also practicing my shoulders. Men feel it when their shoulders are wide, hehe.