What you're saying about throughput I doubt though. The signals are going at what about 1/3 the speed of light? Distance mainly affects latency not throughput. Do a ping test. On a LAN you should get ~1ms (or better) pings if working well enough. Maybe that's not what you mean but that's how I read it. Maybe you did mean that the longer length would cause more signal loss/slower speeds.
I'm not talking about the actual distance. What affected me is that it was going through the breaker panel. The signal strength was affected when it had to go through circuit breakers. If I plugged the two units into the same circuit then I'd get significantly better throughput. One unit downstairs and one unit upstairs would have the same issues as having one unit in the garage. I never really looked into it that much but the only explanation I could come up with was that it didn't like the circuit breakers for some reason.
Houses in the UK are all single phase so I didn't have the issues that houses in NA would experience where the house can be fed with 2 phases.