If you are in turbulent wind you will have times when the furling gets caught out and you may see the occasional burst of high current. As long as these bursts are short it probably doesn't matter much.
If the high current is sustained then it would be wise to try to furl earlier. Effectively you need to reduce the tail moment, that is the weight at the centre of gravity x length. Reducing vane area or boom length will help but you also increase the angle it runs to the wind in normal operation. The only way to furl earlier without affecting this low wind orientation is to use a vane or boom of lighter material ( or change the hinge inclination, which you can't now do).
If you can't use lighter material then reducing the length of the vane is probably your best option, it likely has less effect on the low wind results than shortening the boom.
For steering ability versus weight a tall narrow vane is better than a long lean one and the tall narrow one also will bring the centre of gravity nearer the pivot for the same weight. I suppose a circle has the greatest area for a given weight but I am not sure it has a better steering effect than a tall short vane.
On a different issue I suspect that if you kept the same number of turns your triangular coils have less flux linkage than rectangular ones and it is equivalent to reducing turns or increasing gap, you are getting less open circuit volts and it is keeping you further from stall. If it is working well then you are on a winner.
Flux
