OK, I've just tried the Sanken COS11. Great mic, small (4mm diameter, 16mm long, but OK to poke end out of hat or something).
Very smooth and warm sounding, natural EQ. But there is something wrong with the transients maybe. "Jangly stuff" like tamborine, cymbals, etc, seems "smeared", or lose detail. Believe it or not I prefer Sennheiser KE4 over this. Sennheiser seems a bit colored, but seems to sound OK on everything, including the jangly stuff.
I guess I'll focus on Countryman B3/B6 now. Until then using KE4.
Richard