It is a personal thing to a existent.
If you shot heavy arrows with heavy broad heads you need a long ,high feather. The heavy er,bigger the higher feather stabilizes your arrow quicker.
With selfbows your shots are close so your feathers need to be that way. To stabilize your arrows quickly.
Personally I use HOWARD HILLS ratio 3 to 1 , 3 long 1 wide, 1/8 inch thick (heavy). So I use 5 1/2 ,1/2" high to stabilize my arrrows quick.