Some years ago I had an extended discussion with Mose Nowland regarding the work that was done on TP heads and the flow characteristics in the area where the pushrod tube goes through.
The upshot, boiled down, was that there wasn't significant difference unless the tube was, itself, a restriction to flow. Shaping the runner so that there was no 'bottleneck' at that point got everything there was to get. I called him in the first place to find out what improvement there might be in 'shaping' the tube to make it oval, or pear-shaped, or some sort of airfoil. They weren't able to find any improvement by any shape changes.
This was at the time Brother Lon and I were setting up to use Dove TPs with Jim's 'Type 2' exhaust. The exhaust runners were raised, spaced-out, and re-shaped. I'd have to do some digging to find the numbers now, but they were a definite improvement.
KS