Orbi placement & power level questions

Hello all -

I don't yet have an Orbi, looking to purchase a router/satellite soon to replace an old Airport Extreme for use in a Mac/iOS environment.

I've been following the progress of Orbi (as well as the other "mesh-style" systems) for a few months now, looks like Orbi will be my choice, but a few questions.

I'll be using it in a 2-story home, not large, about 730sq.ft. downstairs and the same upstairs. Orbi router will be in the center of house downstairs, and satellite will be diagonally overhead upstairs. There will of course be a ceiling (plaster and lathing) between them, but the actual distance will be around 15 feet.

I've read that there is a -minimum- distance the router and satellite should be placed, to avoid signal conflicts. Will "15 feet and a ceiling" be too close together? I might be able to increase it to 20+ feet, but not much more than that.

I've read that the signal output strength is user-definable. I'm wondering if I could actually set the signal strength for both router and satellite "down" somewhat, say to 75%? Does the control interface permit this?

Perhaps I could "get by" by using the router only (downstairs), which is how I have things setup now with the AE. But I'll still buy the router/satellite package, to have the satellite available for future use if needed.