Mmmm.....A pro-fesh-enal elk call maker may scoff at my response, but I don't think the barrel length matters a ton. There IS a different sound that comes out of a different length of barrel, but that's just another different girl for the boys to come looking for, right?
I think fitting the reed assembly into the barrel correctly is #1. The reed assembly is not straight, it is a #2 MT, so I use a #2 MT taper to make this a tight fit.
My barrels are 2 1/2" long in general, and have called in both cows and bulls in CO and WY.
Parker