I would expect that the orfice would be formed by the point of the tap drill. I guess if you want to split one down the center, you could confirm that. Perhaps grind or file away to the centerline or close? No, I wouldn't bother.
However, I had a ST "Clone" assembly that didn't shut off completely, and in fact did not appear to bring a Magnum XL .25 to full peak because the NV wasn't threaded far enough. Sort of odd to run the engine with the NV cranked in as far as it would go.
I put that NV Assy. into a .46LA and it worked fine, except that I couldn't shut off the fuel completely...which is perfectly fine with me.

Steve