Spaced air core inductor wire size effect?
The AARL handbook indicates that the formulas are not terribly accurate for VHF small coils. They happen to have a graph showing measured inductance vs turns for AWG 12 wire. The handbook is a pretty useful guide to many things radio-related- even an old one such as the one I have (46th edition). 



When there is some gap between the turns you can adjust the inductance up and down by compressing or expanding the length of the coil.