I think the cone threads on the Pedersoli are 8 x 1mm, like the Euroarms were originally. Pedersoli bought the Euroarms tooling when they went out of business. I would replace the factory cone with a stainless steel cone from Regqtm that has a larger vent. Mine is enlarged to 1/16" I believe. The factory cone has a very tiny pin prick sized vent which they did to prevent blowback when live firing. The factory cone is so hard you will break off titanium drill bits trying to enlarge it even slightly. So that's number one. Change out the nipple/percussion cone.
Secondly, are you sure the flash channel is drilled through into the bore of the barrel? It is rare, but I have seen instances where the flash channel is not drilled all the way through into the bore on reproductions. I have also encountered reproduction barrels where the flash channel is drilled too far back and doesn't line up with the vent of the percussion cone which I think you are describing. Can you bend a pipe cleaner and run it through the flash channel and into the barrel? If so, and you have a replacement percussion cone with a reasonably sized vent, you should be able to get the spark from the percussion cap to the black powder charge and ignite it.
My own Pedersoli Enfield is the very first prototype they made, which was given to me by Pedersoli as compensation for assisting with the design feature improvements when they introduced their new P53 model many years ago. Such things as the correct size .577 barrel, larger hammer, TOWER marked lock, BSAT stock roundel, Birmingham barrel proof marks, correct sling swivels, Palmer barrel bands, etc. Let me add though, not the part about the clean-out screw which they came up with on their own some years later as a solution to reported fouling problems. I advised Pedersoli at the time that the problem was the pin prick sized vent on their factory percussion cone, and that the farby clean-out screw was not what they needed to do to address the clogging issue that was being reported. It was the tiny vent in the percussion cone that was clogging, not the flash channel. I told them the first thing I did upon inspecting the prototype was change the cone out. And mine has never clogged or misfired.
Speaking of the flash channel, on my Pedersoli P53 the flash channel into the barrel is clearly visible when you remove the percussion cone and look into the cone seat as shown in your photograph. I can more or less go straight down at a slight angle with a tooth pick or pipe cleaner and clear the debris during the cleaning process. The same flash channel position (as on mine) is not visible in the photo shown of yours, although there is a bit of a shadow in your photo about where it should be located. If you have a flash channel that has been drilled all the way into the bore of the barrel, perhaps just changing out the percussion cone to a quality steel replacement with a larger vent will be all you need to do for reliable ignition.