Odd skimmer depth observation with sro3000 internal skimmer

I recently changed the water depth of my sro3000 internal skimmer from 5.5in to 6.25inch deep and after a week of skimming it seems apparent that it skimmed better at the shallower 5.5in depth. So contrary to the recommended "better" depth range usually recommended for this skimmer (6-7") my old 5.5in depth works better. Any thoughts as to why this would be the case and has anyone else found a shallower depth to be better for these skimmers?

Oh, and for what it's worth I have my skimmer taking in air from outside and the additional length of air line is about 24" worth and is a size larger (fitting over the existing airline tube that came on the skimmer); with that said I have found no air restrictions over when it was pulling inside air and it has been setup with an outside line for several months.

Thanks

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The depth "recommendation" is just that, a recommendation. That's why they tell you to set your skimmer section of your sump deeper than what you think you will need so that you can adjust the level of the skimmer in the sump. I have two old coralife skimmers that are identical. One skims better an inch deeper than the other. Go figure. Either way, if yours works best at 5.25" then that's where it needs to be. Don't have an sr3000 skimmer so cant comment on the depth comparisons.