Menstrual Cups - Divacup, Mooncup, Instead, Lunette, Miacup

I usually had no problem masturbating while on my period when I used pads.  Now I've completely switched to the cup.  I've read the cup can move up the vaginal canal when you are aroused.  Sometimes I've had trouble getting my cup out as is (I'm using Diva, supposedly the largest; it really sits up there!).  The vagina does decrease in size post-sex but would the cup still be riding high?  Would I have a harder time getting it out?  I don't want to give up my self-desires because that can help shorten your period.  Any tips?

Probably not a good idea to have your yearly checkup with your gyno when you have your cup in.....but I've been reading a few entries and some people have successful sex with the cup in and no issues.  I wonder if the gyno could work around the cup if s/he had to?  I'm not going to try it but I wonder if someone has?