Planetome,
My engine (and the others I have sorted) all have remote needles. My engine also has a partly obscured spraybar fuel entry hole.
Even so the hole is plenty large enough to pass 5 times the quantity of fuel necessary to run the engine at full throttle!

The approach I outlined has worked for me with either the standard muffler or the Tower muffler. In fact the standard muffler gives slightly more fuel pressure than the Tower muffler (the Tower muffler requires a slightly richer main needle setting).

Remember that if it possible to make your engine too rich at full throttle by opening the main needle then you CANNOT possibly have a fuel flow problem and drilling out fittings CANNOT fix the problem. It MUST be something else!

I also simply cannot accept that drilling out the muffler nipple will increase tank pressure AT ALL. Fuel is obviously a far more viscous fluid than air. Since the fuel nipple and muffler nipples are the same bore, it is inconceivable that the exhaust cannot enter the tank fast enough to maintain pressure! We are dealing with an almost static situation here - the fuel flow is relatively low (probably less than 10cc per minute at full throttle) and there is no doubt that whatever the flow, if the fuel can get through the fuel nipples the exhaust can sure as hell get through the muffler nipple to maintain the tank pressure. A bigger hole will NOT increase the pressure.

I actually drilled out my muffler nipple (when I was desperate and before I really thought about it). It made no difference at all to the poor performance I was then experiencing. When I thought about it a bit I realised why!
Why did I drill it out? Simple, I had a totally unresponsive main needle that needed to be about 5 turns open to allow the engine to run at all when vertical. It seemed like a fuel pressure problem. Once the idle needle was set as I have described I was able to close the main needle by MORE THAN 3 TURNS and gain over 1000rpm!!! I then replaced the drilled muffler nipple with a stock one - no change.
I can demonstrate this anytime I want by simply richening the idle needle. The main needle becomes unresposive and has to be opened a number of turns, the full throttle performance falls away (particularly when vertical) and the engine is a dog. It still idles OK though!

The engines I have sorted perform identically horizontal or vertical. My engine is in a fun fly model that spends a lot of it's life vertical. It has great power either horizontal or vertical (no change in revs) whereas it used to drop 1000 rpm when vertical.
The idle needle hasn't been touched for a year and the main needle has only been adjusted about 3 or 4 clicks depending on the weather.