ORIGINAL: lfinney
I wouldn't move the pressure tap , you can count on rossi and novarossi etc and nelson engines to know where to place a tap for pressure and they often place the tap on the header much like yours is, if you own a nelson ultrathrust muffler take a look at their placement of their pressure tap..... you will find that you will have to take at least two or more inches off the header length to be in the right resonance.
ifinney I am supprised you dont know how a ultra thrust muffler works....... The UL Thrust muffler like the jet and the Orginal Super Tiger muffler is a 1/4 Wave mini pipe. These hook up just like a normal muffler but have a smaller inner header that extends back into the muffler. The Pressure tap is installed near the front of the engine BUT BUT in the large Diameter portion of the 1/4 wave mini pipe.
So again to the OP you will need to move the pressure tap to get the most pressure to the tank. Now some people have attained good results directly to the header like that one but noway is it the best.