There is a fundamental problem with erotica. When the characters are compelling, the couple is enchanting and the plot is well delivered, there comes a point where you really don't care about how the characters have sex: you just wanna see where they end up.
And this doesn't get better with long series like this. That's why I found myself skipping most sex scenes. I couldn't care less how Sophie and Neil had sex. The gay that BDSM is so over right now doesn't help.