Unders are said to be more natural, but like you say it does depend on what tissue you have already.
As for the gap in betweem your breasts, if you already have a large gap, chances are it will be there when you have the implants. Likewise if you don’t have a big gap, you will have even less when you have your BA!
Check Fairyxx’s piccies, she had unders and they are amazing, so natural *jelous*
I’ve not had mine by have the same fear as you. I want to look totally natural but VERY blessed.
Mr Kazazzi suggested 460 hp unders from a 34b
xx