I agree with you, external oblique and abs vary from individual to individual. In my opinion, I think that watching a lot of references is very helpful. Look up pinterest for body builder torsos and sketch them. I guess that, in time, you'll build a visual memory of this part and will be able to incorporate it when you draw from imagination. That's what I would do (and what I actually do :)). I hope you can pass your block. @Isaac Litman
I understand that the external oblique and the abs can differ quite a bit from individual from individual. But I really do feel stuck when trying to best figure out how to draw the external obliques' relationship to the abs when drawing from my imagination. I've seen some people just design it as if the external obliques directly connect to the individual sections of the abs, and other people connect one or two of the striations to the individual sections. Wonder if anyone can provide advice, so that I might be able to get past this artist block. I have attached some examples of images showing the external obliques interacting with the abs in very different ways.