Alright, I am an idiot.
After what Heath said, I retested my system. The issue is a 15m cable using 1mm^2. That is rated to 11A depending on the conductor, but at 10A, the voltage drop over the whole length is 2.55v, The battery is only "seeing" a lower voltage, hence lower potential difference between battery and charger, and lower charge rate.
I've unfairly maligned this charger. My apologies.
eBike: Q100H on 16S with Phaserunner FOC Controller
eMotorscooter: Vectrix VX-1 on 36S
eCar: Mitsubishi Outlander PHEV... Waiting for warranty to expire
eHouse: Still on grid, but with LTO batteries and 3kw LF inverter...
After 5 builds, the best advice I can give, is start with high quality products. I prefer http://www.ebikes.ca