[Delphinus]

(Do I count as a beckett user? Or a bullet user? It's almost the same thing.)

I have my water/air interface approximately 1/3 up the reaction chamber.

If you look at all the beckett skimmer designs out there, you'll notice that there tends to be a lot of differences in terms of size of reaction chamber/size of riser. This is a little suggestive to me that guesswork is a big part of things even with the manufactured models. When you get down to it, if it works then it works, but it's really hard to compare two different models and determine that "model X" has 1% better efficiency than "model Y".

Basically I think you want your riser to be full of foam (no water that high). Adjust it from there higher or lower if you want a wetter foam or a drier foam.

Does this help at all? I'm thinking probably not. If you have any specific questions fire them away and I'll do my best to explain what I do (not that it's right or wrong, but I just generally do what seems to work well enough for me ... I'm not that fussy when it comes down to it).