Wanting to fill my cleavage/chest and have a more natural projection - Choosing between Mentor mod+ or HP?

It is important for patients to understand that augmentation will "augment" all aspects of your anatomy. The spacing of the footprints of the breast on the chest wall will vary from one individual to the next. Widely spaced breast will appear more widely spaced and vice versa.
The spacing (cleavage) is defined by the pocket. The pocket is defined by the plane of augmentation.When placed submuscular, the medial/middle limit is the sternal origin of the muscle. Wide sternum greater separation of the breasts less dramatic cleavage. This space can be narrowed (with some risk of synmastia) when the devices are placed subglandular or "over" the muscle. There is no muscle obstructing a medial push, however, there is a higher risk of over-dissection and midline migration of the implant (the dreaded "uni-boob").
With regards to your specific question, a higher profile device is narrower but will project more. A wider device can create the illusion of closer spacing between the breasts (when placed subglandular). Most patients will fit into the "moderate +" category...but this will depend upon the measurements of your breast width. That being said, it is never recommended that you stray far from your unique BWD.
And remember...love the look you choose...not the cup you desire.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

After I measure and discuss goals with my patients, we then look at pictures of women (my patients) with similar measurements with different size and style breast implants. They also get to see what they would look like when the breasts have fully dropped and fluffed and in clothes. You get to see actual results and the surgeon's experience and not a virtual idea of what can be achieved. Women tell me that this process is very helpful in determining what size and style breast implant is right for them. Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author. RealSelf Distinguished Hall of Fame Inductee. Philadelphia, Pa., USA

The technique I recommend is The Bellesoma Method. This will reshape your breast tissue creating upper pole fullness without implants, elevate them higher on the chest wall and more medial to increase your cleavage. Vertical scars are avoided, nipple sensation (in 95%) and the ability to breast feed are maintained. Later, fat transfers or small implants can be placed if additional volume is desired.

Best Wishes,

Gary Horndeski, M.D.