11.7cm or 11.2cm Breast Implants for a 13cm BWD?

Since you are having a periareolar lift, there should be some caution and concern about using a implant that may be too large or too heavy...that form of lift does not support large implants well.
So the voulme of your implant (in cc's) may limit your implant width choices. If you want as much cleavage as possible, then an implant that is slightly over your BWD may be OK. On the other hand, the perioareolar techniques tend to flatten or truncate the breast some, so a higher profile, narrower implant may be required.
As long as your doc knows your aesthetic desires, and you know the possible limitations, you should get te results you want.

I am sorry to say this here but it is not your final responsibility to choose the right. This is what you board certified plastic surgeon needs to do. You job is to describe and convey to your surgeon the look you are going for and what you would like to achieve, even the ballpark of size wise what you desire.
But the ultimate decision needs to be in the hands of your plastic surgeon as he or she has a lot more knowledge and experience as to what would work better for your body.

Without the benefit of examining you, the implants should be within 2 cm of your breast width. Going smaller than that would create a very bizarre appearance. Keep in mind that there a variety of implant volumes and projections that would have the correct base diameter for you, so you should be able to achieve your goals without going "too big".
Choose a Board certified plastic surgeon who performs breast augmentations frequently. If you have adequately explained your goals to your surgeon, trust him or her to choose the right implant and provide you with the results you're looking for.
Good Luck!