Not all flintlocks are setup properly...The touch hole should actually be covered by the edge of the frizzen closest to the barrel when closed...This ensures that prime doesn't get into the touch hole...Some factory flinters have the touch hole set too low...(Below the top edge of the pan)...In this situation the priming could actually be covering the touch hole when loaded and the priming has to burn below the touch hole to ignite the main charge...This is why you experience delays...It also helps with these setups to tip the rifle before you shoot so the priming slides away from the touch hole so you don't have the fuse effect...

But of my flinters are custom and it doesn't really matter if I use a half pan or a full pan...Because the touch hole is in the proper position...