How much more of a risk of capsular contracture is there with implants above the muscle?

Thanks for your question, which is a good one. All breast implants will form a capsule around them, and the degree to which this is likely to contract is thought to be related to a number of factors including implant surface, placement, and implant contamination.
Lower rates of capsular contracture have previously been reported with implants put underneath the muscle, but this is partly due to the implants having more coverage and therefore when capsular contracture does occur it is less likely to be reported by the patient. Implant technologies have moved on significantly, and the risk of capsular contracture, even with a subglandular augmentation (in front of the muscle) is low. There are a number of advantages of subglandular placement that you may feel outweigh this risk.
In my practice, getting the implant placement right for the individual patient is important, and the risk of capsular contracture is one of a number of factors that will feed into this - the risk/benefit profile of each of the decisions that you make about your implants (surface / shape / dimensions / placement) should be discussed with your surgeon and individualised depending upon your priorities.

Capsular contracture can occur with implants placed both above and below the muscle, but below the muscle simply carries a slightly lower risk. If you want implants above the muscle and you are a good candidate then it's fine to proceed as planned. I've included a video on capsular contracture that I hope you find helpful.