Large spiral feathers go a long way to stabilize an arrow at close range. I am not entirely sure what causes fishtailing, incorrect spine (dynamic stiffness), will make arrows fly left or right of where you want and fishtailing is probably part of that.
In bow hunting close shots are the rule. An arrow flying a little slower, but flying straight, will give better penitration than one flying sideways fast. That, along with the planing effect, is a reason for big feathers.
The arrow/bow set up can be funny. The most accurate arrows I have shot from my bow used 5" high parabolic fletches and sported 100gr broad heads. When i swapped to 100gr field points they didn't shoot as consistantly.
If you use modern equipment it is much easier to get say 24 arrows that accurately match your bow. If you are making your own bows, and are both learning, and trying new things, you aren't going to get arrows that are that well matched to your bow. Bigger feathers will slow your arrows, but make them more forgiving of differences between one bow and another.
I have found that at short ranges large helical feathers were on average more accurage than same size straight feathers, or low cut helicals. At long range the low cut helicals dragged less and shot flatter than the high cut straights, but there wasn't much to choose for left/right accruacy.
Why not start with long high cut fletches, and experiment by trimming them shorter and lower until you find where you are happy?