what would be the best way to blend 20 layers in a single composition so the layers have equal opacity?
Im not sure how exactly opacity stacks (10 layers, each with 10% opacity is still quite transparent).
I would appreciate any insight into how it actually works
Set the blending mode to Alpha Add for linear transparancwy accumulation and then do the math. The default blending uses a multiplication formula, hence things will never be 100% opaque if the values are linear.