I use 7/32 for the eel that is produced by folding and tapering a single length (whole) of material. In other words, take a full length swatch, twist the end like a moustache, then fold it. Twist the joined ends again to ensure a lifelike taper. That's the length. Your unused material stays in a perfectly square cut manner on the bundle that way. This amount of materials times two (at least) creates the ratio I mentioned, in fact it might be air resistance that makes it seem to cast without a slingshot effect. These eyes are not lead or tungsten and aren't all that heavy but they do put the point out of the crap on the bottom which is critical in flats fishing.
For smaller eels (more the case lately) I go to the smaller sizes which escapes me right now. I cut the swatch, fold, but tie it in further down away from the fold for small eels.
Good luck tying them up.