OK, I see now.
It will be hard to have an elevated water level, and thus the skimmer higher and still have a low cap, unless the skimmer cup sticks out.
If using an ATO, the water level could be lower as you mentioned and then the skimmer, {again not sure on nano skimmers}, could be run in supm mode, sitting on the tanks bottom. Its also not water level specific in this mode and the cap could sit where you wish it then.
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Doug
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