For a uniflow tank, the point where the uniflow opens into the tank.  That tank doesn't look like a uniflow, however, so for that one I'd say the centerline of the tank.

For profiles you often want the tank about 1/8" higher than the hole in the spraybar to start, and then adjust from there.  Without muffler pressure, however, I think it's all moot: check back with us when you give up and go to a uniflow.

This is neither uniflow nor pressure.  It is being used with a Brodak 40.  I do understand that the 1/8 above works with Fox 35's.  I don't know if it applies to other engines.

  Start with it a bit above center, then move it to make the upright/inboard laps times equal.

    Brett

Sounds like center line of tank.

Thanks Brett and Tim,

My question is answered.  Center line of wedge will be slightly above the needle aperture.