I have had one for many years now. Manual states 4 3/8th" from LE of the wing.
Mine has an OS FT-160 twin fourstroke in it. 17lbs AUW.
Manual the 1/4 scale Cub can be flown with a .90 2 stroke or a .90 to 1.60 Fourstroke. I would suggest the Fox .78 to be a tad small. Small gasser of 26 cc would be a good choice too.
Good luck.