Thought I'd figured it out, and slipped today

K3D N+, to an N, #3 curved, to a 2.5 curved, to now a #2 curved bent to a gap of 20mm, and thought it was perfect - until today a ball slipped. Bleh. Same old story, seems perfect, and then there's either burning (gap) or a slip.

Do I try a #1!? I seemed to have learned not to buy the 2.5 prematurely...