Just looking for scenes where one guy has a bigger dick. It's mostly NTR, but there are some that aren't. The two guys don't have to be in the same room at the same time. Here are some:

Houkago rankou chapter 1 (NTR)
Nitta jun, prefectural centre... "tied up" chapter (non-ntr)
Nitta jun, kimi-tachi doumei chapter 2 or 3 I think (NTR)
ver9, She chooses her man... both chapters.

Ty in advance

There is one by Nagare Ippon called "I Will Protect You" that has that element.