Different controllers have different input voltage limits
With a 57v input limit
You could series 3 16v panels, but Not 3 22v panels
You can parallel panels with different voltages, but you do get some voltage averaging at the input, so the closer the panels are in Output voltage, the more efficient the system well be, this holds true whether the controller is mppt our pwm
The lowest AMP panel is a series circuit, will limit output to that amperage as max possible, series panels need to be the same amps rating to have a efficient circuit
Example think of 6 ft of 1/2 water line in the middle of a 30 ft run of 3/4 water line, the 1/2" limits the water flow
And it doesn't make any difference, middle or end of run, it restricts the flow