i have chased my tail on this for years, and i dont know if there is a definitive answer.
in the end, i focused my energy on getting a really good bare shaft tune- got my spines all within a pound or two of each other, then with a well tuned shaft, i felt i could go with shorter , smaller fletches_ i use a 4" fletch, and certainly no higher than 1/2" at the high end of the shield cut.
and i could then also reduce my angle of helical- i still want them to rotate- but the less helical there is, the less drag.
i really work hard at getting the shafts really straight, and i get the broadheads properly centered and the glue on nocks properly centered- that way i feel that i can reduce some of the helical.
its all a trade i geuss- if one is shooting wide , heavy 2 blade broadheads then i would think more fletch would be advisable.
i like to shoot 3 blade heads- 1. cos i like the hole they make, and 2. i think they are less prone to planing-
i do need to use shields as they are part of my anchoring system, but from all i have read the banana cuts will produce less drag and less noise.
another thing i strongly believe in, is putting a tail taper on the shafts( well most of you guys shoot , shoot shafts anyway- so they came pre tapered
) as one takes mass off the rear of the shaft, one is inadvertently improving the foc, on a std shaft its a ratio of about 1 : 1.6 .
so if you take 10 grains off the rear of the shaft- its like adding 16 grains to the front.
the increase in foc- (without actually adding weight to the front) helps an arrow stabilize quicker- and that in turn helps justify a reduction in fletch size. as i am relying on the well tuned shaft, and the higher foc to do most of the stabilization, as opposed to big ol' fletches dragging the shafts back into alignment via the use of drag and rotation.
we also have very wind conditions here where i hunt- and i seriously worry about the arrow weather vaning in a cross wind- smaller fletches also help in that regard.
anyway- i dont know if all that mumbo-jumbo helps at all- just my .02c on the conundrum!
i did a lot of tests, on how to improve the FOC, without actually adding mass to the front of the shaft, as i did not want excessively heavy arrows- just good 10GPP arrows with a good foc.
helping to facilitate better penetration, better recovery times, and reduced drag on the stern.
i have those results from those tests- if they may help you
