I store with nose up. I run 2 strokes but I am sure this holds true for the 4-c's also.
Reason being, the residue in your pipe will settle into the engine. This residue is all the gummy byproduct from your combustion chamber. This residue contains acids and gunk not need in your nice clean engine. Any fuel in the pump can migrate to the carb also and raw nitro is not good around the bearings. Al lot of people use after run oil. I just run mine dry and store with nose up. So far so good. Last engine had over 400 flights on it and still has original bearings in it.

Wayne