Is it a bottom bait, pop up, or balanced? Also what rig material are you using, and how long is your hook link? Is the bait really thin? What hook size?
To my mind, hair length just comes in with a whole other list of variables that affect rig mechanics, and one affects the other and so forth.
its a bottom bait, the rig material is coated braid with abit stripped back by the hook. the length is probably slightly more than 4 inches the bait is probs slightly less than half a millimeter in thickness and the hook is a size 10 korda kurv shank hook.
Wow, that is a thin bait!! With a 4 inch rig I wouldn't go too long on the hair. The bait hasn't far to move before it will hit resistance and you don't want the whole lot being pulled back out of the mouth before its been sucked in properly. Too long hair on a short rig and the hook might not be in the mouth before the fish realises its not just a freebie. 5-10 mm from the top of the bend in the hook to the bait, but that's just my opinion. Others may differ. Maybe a blow back type rig too perhaps, or some tubing on the hook to keep the hair along the hook until past the point?
Doubt there are any hard and fast rules for a bait that's less than half a mm thick! Is it like a sheet or something? I'd have a play around with different set ups and see what works. If you think you're missing pick ups or getting aborted takes then change the hair length or rig length.
i think i got it wrong half a millimetre isnt right not sure how thin it was but not that thin. i ended up blanking anyway. not sure what was happening as i was getting bleeps and what seemed like semi takes. i dont know if thi was carp or other fish?