I'd normally leave 8-10mm from the bait to the hook, but that can change depending how you tie it.
Two identical rigs below with hairs done for 16mm baits, hair extenders work to a degree but i find that awkward with hard or plastic tipped baits,
solution, bait floss, cut a 5-6 inch length , pass through the hair and double up, put baits on needle, loop over floss and pull through,
one will be on the hair, one on the floss, a few overhand knots and a baitstop if required, voila same rig ,double bait, snowman etc.
If i'm using a heli setup, then the big eye quick change swivels are ideal (bottom of the pic) coupled with a A.T sleeve,
This is also useful when you have a fish in the net, unclip the rig take the rod away then sort the fish out on the mat, saves trying to carry both if your on your own.