I don’t think altering the number or size of the feed holes will have much effect, I’m pretty sure the pressure between the inner and outer chambers will equal itself out. Saying that though … I can see that smaller feed holes could be a benefit as you get towards the end of the fuel, as a smaller hole will be below the fuel level for longer which might help maintain a higher internal pressure in the outer chamber towards the end of the burn. 😯
I suppose the obvious way to increase internal pressure would be to reduce the internal size of the stove and/ or use more fuel (which would reduce the internal size) … obviously the pressure would start to drop as the fuel was used. The other option as you say, is smaller jets … restrict the gas getting out and the internal pressure must increase.