I was just reading some interesting articles on modifying the touch hole (vent liner).
One article showed an illustration showing a drilled cone on the outside (toward the pan) and a slight chamfer inside (toward the main charge) leaving about a 1/16" long flash channel. The flash channel dimensions varied from .050" in .45 caliber up to .062" - .070" in .54 calibers and up. The flash channel holes were gradually increased using numbered bits. A touch hole modified in this manner, according to the author, didn't matter if the pan charge was "banked" against the touch hole or away from it. In fact ignition was actually faster when banked against the TH! The reason was that the pan charge was virtually directly in contact with the main charge so there was no fuse effect.