Subglandular Style 410 implants for thin/muscular build
Taking into consideration the things you do not want, then I think that a shaped cohesive silicone implant on top of the muscle is a way ti go. Having said that, you should ask to feel that implant as it is not going to feel as soft as the other silicone implants out there.
Subglandular Shaped Implants
I think you are on the right track. The two options I would offer you would be a subglandular shaped implant as you mentioned, or submuscular, but an oval implant so the upper pole does not have as much muscle effect when you contract. You probably need this shape implant anyway because of your strong pec muscle and upper chest shape (from the pictures you sent). The choice between over and under the muscle would be based on how much tissue you have in the upper part of the breast.
My preference would not be to use the 410, because it is too firm, especially if the implant is subglandular. I would choose the Sientra Oval Shape, which is softer and has great options for size and projection in the Oval. This would allow you to control both your overall size, and the uneven size and shape of your breasts (seems like from your pictures).
Obviously a full consultation is needed, but you definitely have the right idea.
Best of luck in your research.
Thank you for your question and photos. It is uncommon to place a subglandular implant on a patient who is very thin because of the increased visibility of the implant and the increased risk for rippling along the edges of the implant. Your concerns for placing the implant above the muscle are valid ones, however. If you are going to place an implant in a subglandular position, the best implant to use is the shaped highly cohesive implant, such as the style 410. That is a good choice and will give you a very reasonable result.
Subglandular Style 410 implants for thin/muscular build?
Unfortunately, I think your plan is a recipe for failure with bad results and wasted money and a difficult problem to fix later on. I see too many patients that had that done and are very unhappy. There are no shortcuts to good results, so if you don't want the subpectoral placement, skip the implants.