I like the gestures! For the width of the abs, it changes from person to person, but I find that usually the appearance of the rectus abdominus follows the shape and type of the body. For example, on long and slim people it appears longer. On fit, sort of boxier, people it appears wider and more defined. I drew over pictures to try to give you an example. Another thing is that it looks like you’ve drawn the upper body too wide (and/or not long enough), maybe that could contribute to making the abs look out of proportion? As for the top part of the abs, its the most irregular and definitely it isn’t easier to find they’re shape at times since some parts are under the pec major. Maybe try looking for patterns or common shapes throughout your studies could help you in being able to design them more easily. Hope this helps!