Yeah so I think this might be it. I'm running 18AWG from the strips to Wagos but 14AWG between Wagos. However, and I don't know why I did this, but I am running the 18AWG from the driver to the strips. Seems I stumbled at the last hurdle of this build haha.
I'm pretty new to this stuff and honestly starting from scratch with building stuff with my hands so I was super proud of myself that I got it all up and running with aluminium heat sinks and all!
But yeah, I'm surmising that the smaller gauge wire carrying all the current between driver and strips is increasing resistance at the 'start' of the circuit, thus decreasing current at the constant 20V.
Queation though, if the strips are still getting their 19.9-odd volts across each of them, I'm assuming that they are still actually pulling their associated current (according to the datasheet)? Ie. If I was to measure the current running through an individual strip, I'd see 0.5ish Amps?
I'll swap out the 18AWG wire at the start of the run for the 14AWG anyway, but just curious..