How important is the vertical offset from receiving and transmit antennas? We deal with a lot of homes that are not multi level and getting a 15ft difference would be difficult and maintain HOA approval.

That said, I've never been a part of an install of any brand that has impressed me in any way. Only time I've ever been impressed is a macro cell from a cellular provider.

Vertical offset is important- not enough causes problems similar to it being too close.