How do you figure the maximum input current to make sure you meet the inverter's specs?

Do you use the short-circuit current or the optimum operating current?

Do you multiply by 1.25 for high irradiance (like NEC)?

Do you multiply (again perhaps) by 1.25 for continuous use?

Is this per terminal for the input or total?

[I'd think you use the short circuit and multiply by 1.25 once and it's per terminal, but just checking.]

Another question -

If you have 3 equal strings going into a Xantrex 4.0 which has 2 sets of terminals would you combine 2 of them for one set of terminals and put the other string in the other set or would you combine all three and just use one set of terminals?