My personal opinion here after studying many pics and seeing them in the real world, of over and under the muscle implants (saline and silicone) in women lifters, I just don't care for under the muscle. Too much lateral projection that leaves a big gap in the center of the chest, too much movement when the pecs "flex", many times producing a very unnatural look (implants jump all over), and development of a pocket under the pec with considerable movement of the implant, plus the pec gets ripped up during surgery.
Ripples are minimal with silicone implants and they give a much more natural appearance (tear drop effect). Even under the muscle salines will show ripples where the implant meets skin.
Having said all of that, I have seen a few, key word few good under the pec jobs, but not usually in muscular women.
The surgeon knowing what they're doing relative to your needs and body type is also critical.
Just my two cents.
W6