Do you wear your marksmanship badge when wearing full sized or mini medal(s) on class a ASU?

No, because the medals will cover the top of the pocket and I have never seen anyone wear marksmanship badges above their ribbons, that's just crazy. Marksmanship badges are always worn on the flap, see section 29-20 [AR 670-1, page 283, version 2005]

per regulation: "When full-size medals are worn, up to three full-size or miniature combat and special skill badges from groups 1 to 5 are authorized for wear above the medals, in order of group precedence (see para 29–17a). Males may not wear the Driver and Mechanic badges with full-size medals, and they may not wear special skill and marksmanship badges on the pocket flap below the medals (see fig 29–4)." [AR 670-1, page 271, version 2005]

thank you for your service and always remember when wearing your uniform in public to check with your team/squad leader BEFORE you head out.

Most take it off when wearing complete medals. Good luck staying cool at the service tomorrow!