Dan.... I am "Almost" certain, without looking or seeing your airplane that it is slightly tail-heavy. What you are going through is what many pilots experience when performing the Hammerhead with a plane that has a rearward CG.

Some pilots prefer to have an airplane that requires very little (if any at all) down elevator when inverted.... I know...because I used to trim my plane like that....but you will find that a little forward CG on the airplane will work WONDERS, not only on many maneuvers (including snaps)...but your Hammers will be a thing of grace!

Try adding some weight to the front the next time you go out & see what happens...you can always take it off if that does not fix it for you...
Let me know how it all turns out.

Wayne

PS..... I would suggest keeping the low rudder settings you have for sequence flying, but definitely use a switch for the Hammer..... It is something you are going to need as you move up the classes, so it's better to start learning switch changes from now.