Bra cleavage!

In my opinion the possibilities for cleavage depend more on the shape of
your chest and rib cage than anything else.
This factor is only very
rarely mentioned in surgical assessment but is absolutely vital in
terms of determining how likely you are to close the gap between the
breasts.

So... if your ribs slope away quite a lot it is more
likely you will start and fisnish with a significant gap between the
implants and there isn't a whole lot that can be done about this.
If
your ribs are pretty straight then you are more likely to start and
finish with less of a gap.

You are also right that changing the
profile or base width of a form-stable implant can push the implant
closer to the middle - especially in the context of a secondary
procedure when the lateral wall of capsule can be used as a resisting
buttress to push the implant toward the middle.

The most
important factor though is undoubtedly chest shape.