small quibble - the FM60/80 manual provides a graph of efficiency for a 24V battery setup. (No corresponding chart for 48V). For 100V input, which is almost on the mark for these panels at Vmpp in a 2S configuration, the efficiency is 95%. So it would take 4200W input to provide 4000W = 80A x 50V output.
Others may take another tack, but I ignore conversion losses because:
#1 they are hard to compute,
#2 they generally are internal to the circuitry, so mean they are causing things to heat up.
Overdriving the input to make up for losses adds more power to the losses as well.
One should do what one thinks best. I tend to err on the conservative side.
The controllers will limit output to their current limit settings - eventually - but will overshoot them if the input is overdriven. If one watches closely, it can be seen, even under "normal" circumstances. Resonse to an increase in input power is not instantaneous.
the controller limited output current to the value I set in the controller
If the input is overdriven hard enough, the controller will actually lose control, and dump the raw input to the battery. I've seen the results of this with my own eyes, and fortunately for me, not to my battery. Let's just agree that feeding over 100V to a 48V battery can have catastrophic consequences.
I'm not exactly convinced Current Limit = 80A actually engages the current limiter. There are many "magic" patameter settings in OB gear that aren't commonly documented.
My favorite is all the activity behind the REBULK parameter.
Another is Absorb Time. Of course, a non-zero value for Absorb Time causes the controller to run the Absorb phase for that period of time.
So what does Absorb Time = 0H do?
Skip the Absorb phase, you say? Partially correct. However, it also causes the controller to skip the Bulk phase and go directly to Float when it starts a charge cycle.
With that in mind, I'd expect Current Limit of 79A to engage the current limiter function at or around 79A. Current Limit = 80A? I'm not so sure.