I currently have only one Ilmenator's TPD attached to RX PCB after 3m of cable.
At TPD PCB I have a voltage of 4,35V, but it still works as expected. On TX PCB (before 3m cable) I have 4,6V, so already some drop from USB input over all the PCBs and cables in the main SEQ assembly. And voltage drop over 3m cable and RX PCB is 250mV.
Rowan: Do you mean your display contrast is reduced? Or the brightness of LEDs is less? All of them or only on remote PCBs? How are your levels of voltage on main / remote PCBs?
Generally, the suggestion from Rowan is worth thinking about - and maybe necessary for bigger remote installations, but from my side I did not see any issues with the current solution and maybe there's a different solution possible without changing all the documentation.