I tried the big mushrooms, front and back, and for me, the smallest to keep it in the sight worked the best. I thought a big ol mushroom would work best as the front sight is what I focus on, but it didn't turn out that way. You may be different.I checked mine from the center par of the rod. I'm going to try to leave a bit on the back side of the sight before heating to see if I can make the front end a bit larger and how it would look and function.