[Radio Wrangler]

Remember, your inductor is not a pure inductance, there is distributed stray capacitance amongst its turns. This distorts your inductance readings and apparent resonant frequencies, especially as you approach the self-resonance frequency. Modelling errors can get out of hand and rather counter-intuitive things appear to happen. 2-layer coils really make the capacitive effects worse. expecially if you laid the turns out there-and-back-again-over-the-top.

David