I don't really know the rights and wrongs of roost height, but what I will say is that we still use the same system my grandfather used many, many years ago and it has always worked for us. Our chickens live in a walk-in shed and inside is essentially a long table with a ridged ramp for them to walk up on to it. On the table are two milk crates, one either end, with the perch resting on top of them. The perch itself is actually a pair of perches but joined at both ends... it looks a bit like someone has laid a ladder down but taken out all the rungs except the top and bottom if you see what I mean.
Chickens of all shapes and sizes have been OK with this set up and they can all get up there easily. They just walk up the ramp and then hop up onto a crate and walk along or jump up onto the perch itself. Some of them cosy up with King Olaf whilst others spread out. Since I have been more involved in the chickens I have been grateful for the set-up, as I can just remove the perches and crates for cleaning, spraying for mites etc. It's not fancy but it is convenient.
ETA: our nesting boxes are at floor height so significantly lower than the perches. The table format also means that the area of floor underneath the perches stays clear.