I was surprised to learn of the existance of the optimum coupling with respect to the best performance of SG coils.Dr.Resonance tells that the optimum for his coils is about k=0.13-014.Before that I just thought tighter the coupling better the performance and the only problems with tighter couplings were racing sparks and flashovers.But even if the conditions are such that secondary itself is free from undesired discharges ,beyond certain coupling point spark lenghts might start to diminish!Contrary to what I expected.Well,Dr. R makes all his coils with aspect ratio of the secondary H/D=4.5..and I suspect the systems with different H/D parameter have different optimum couplings.H/D ratio is not only thing to consider in respect to these matters but is a good candidate to put on test.
Dex