Somewhere on Leaper's website it lists what mount height with up to what size scopes.
If I remember they state the medium height Leapers mounts are good for up to 45 mm. Based on that, when I ordered my Leapers 3-12 x 44, I also ordered the medium height one-peice mounts. And like with triry's 50mm and high mounts, my Leaper's flip-up cover just clears the reciever, but it does clear without any problems. The 40mm with medium mounts should have no problems either.
Paul.