I don’t think unders vs overs makes much difference in terms of closing the gap! I f I were you I’d ask your surgeon for your measurements in terms of how wide your breasts are, and then have a look on the implant manufacturer/s website and get the measurements for all their implants.
That\s what I did! I knew I was having Mentor high profile type 2 cohesive textured implants. So I found the catalogue thing online that had all the measurements of how wide each cc of that implant is, and I purposely went a bit bigger than what my breast width was, so I could minimise the gap. Definitely switch to moderate too as they’re even wider than high profile!