My understanding of running rigs is that you're not relying on the lead to do the hooking. So weight is irrelevant except to get the distance, guide the line and provide resistance to the bobbin to give indication. Using a heavier lead can cause more problems getting plugged in silt, light weed or clay and clog the run ring effectively creating a bolt rig.
If you re getting takes, I'd probably look at the rig and tweaking it as you're obviously doing something right. You say you've tried longer hairs, how much longer? Have you tried doubling the seperation? Say 5mm at a time? If your catching it's probably minor changes that will make a difference so whether it's hook, hair, line alined do it one at a time so you understand what's been changed and the effect it has.