There are some topics on the forum with regards to daggers, but placement is at the top front of the well, and bottom rear of the daggerboard well. The biggest thing I've found is technique, pulling forward and up rather than just straight up. I have put Velcro on mine, and it helped but was eaten up pretty quickly. A friend of mine is utilizing some neoprene and 5200 and is pretty happy with it.
Your jib sounds like it's either worn, or you may have too much foot tension. You can play with it on the beach(without too much wind) and just manually grab the tackplate and pull down, pull back, and pull down and back at various places to see how to trim the sail. You want even tension leach and foot. The shape of the H18 jib is such that you can crank on the foot and create a flap, I think this will only happen when the sail is a bit worn out, still usable and maybe cosmetic, but has lost some of its shape holding potential.
Fleet 259, Central Coast CA