I think somebody already mentioned this. But it may be your torch orifice is just not quite the perfect diameter for the tubing you're using. I've heard aircraft builders complain about this many times.
All I know is that ONE time, while completing a square cube in a recent welding class, I got exactly the right torch size, the right flame, the right initial puddle (a bursting fat one) and boys, I hit the groove! Of course it was 3/16" plate and not paper thin 4140 carbon steel tubing.
But every seam on it was pretty near perfect.
Therefore, "if I were me" I'd adjust the flame from the regulators never mind what the needles say. I'd get the blue flame tip where it would instantly turn the metal shiny and produce a puddle within just a few seconds, make sure my initial puddle was plenty turgid, and weld away. If that doesn't do the trick I'd go to the first size tip that's too small and ream it to halfway between that nominal tip diameter and that of the next larger size.
But if you're doing aircraft clusters your skill is already light years ahead of mine.
V