why the far end of the run is browning out.
drop = 2 × length × Ω/kft × amps ÷ 1000 (round trip through both conductors)
planning math for copper at room temperature — not an electrician, and neither is this calculator.
pick a gauge from 6 to 18 awg, put in the one-way run, the load in amps and the voltage, and it returns volts lost in the cable, drop as a percentage, what is left at the fixture, and the longest run that still holds 3%.
drop = 2 × length × Ω/kft × amps ÷ 1000, doubled because the current makes the round trip through both conductors. that is copper at room temperature; cable baking on a black deck in july reads worse.
3% is the target and 5% is where things misbehave — tungsten goes amber, led drivers flicker at the bottom of a fade. go up a gauge before you shorten the run; most stage extension is 12 awg and runs out of road early.