Any real upper pole difference between SRX and SSX when under the muscle?

You're thinking is correct. The different gels that natrelle implants are available in can theoretically change the amount of upper pole fullness as shown on their website (link included). But this would likely be much more visible in either a subglandular (on top of the muscle) breast augmentation or a breast reconstruction after mastectomy. With the muscle on top of the implant constantly pushing down on it, I doubt there would be much day to day difference in how they look. If anything maybe (but probably not) between the SRX and SCX (response vs cohesive) but I doubt you could tell a difference between response and soft touch. I bet if someone did a study having plastic surgeons look at under the muscle augmentation patients with the same implant but different gel types they probably couldn't consistently tell the difference.
All very confusing and nuanced but I hope this helps!

The implant projection doesn't change the upper pole projection because, when the implant is inserted in place, the implant drops slightly because of gravity and implant weight . A standing or sitting upright position, the implant's gel distribution reacts to gravity. If the patient's skin has a good quality and it is tight after breast augmentation, the upper pole will always look fuller and firm . The difference between one projection and another is minimal . When using the dual plane technique for implant placement, the muscle covers any rippling effect that often is visible. The muscle will not improve the upper pole fullness. The upper pole fullness is basically being created by the pressure of the soft breast tissue against the implant keeping a round shape when standing up without a bra but, the use of a bra will support the weight of the implants providing longer lasting "Perky"results . I hope this has proved helpful, and I wish you the best.

The difference would be very subtle and depends on how much tissue you have over the implants. Theoretically the soft touch implant would give more upper pole fill. The extra full profile will also give maximal upper pole fullness

The feel of an implant in one’s hand does not precisely translate to what the breast feels like with this implant or that, especially when under the muscle. Ask yourself if you want the softest possible breast or slightly firmer, but the difference is essentially imperceptible. Best of luck to you.

The higher the profile, the more the implant will project from the body. However when considering the same volume implant the higher profile will not have a significantly different look when placed in the body. It would be a subtle difference. I encourage you to discuss your concerns with your surgeon as it is important to be comfortable and confident as you prepare for surgery.

The upper pole fullness will depend on several factors including implant volume, gel stiffness, width, and how much native breast tissue you have. For the same volume and width, a stiffer gel (the soft touch in this example you gave) will maintain more shape in the upper pole when standing up. The question of if it is noticeable once you factor in the effects of your skin, breast tissue and muscle in front of it is a difficult question. The short answer, if we are being completely honest, is we don't know. They did not do those studies within the body. If you have thicker tissue, it is less likely you would notice a difference (imagine the difference between seeing something under a comforter vs a sheet). In either case, the differences tend to be subtle in real life.

Quality breast, augmentation results are generally raised on three different variables. Each of these variables are probably equally as important.
These are.1) the patient candidacy for the procedure2) proper selection of implant in regards to type, size and shape.3) placing the implant in the anatomically correct position.
Each plastic surgeon will have their own way of helping patients Choose the right implant type size and shape.
There are a lot of variables to take into consideration. I suggest you follow up with your plastic surgeon if you have questions about implant selection.
If you haven’t chosen a plastic surgeon, then I suggest having multiple in person consultations with providers in your community.
Best,
Mats hagstrom MD