Apex 300 Power Input Question

I have an Apex 300 which I’m using to power a transfer switch. Although I’m on 240VAC North American split phase, the transfer switch is wired for purely 120VAC circuits. I’m powering the transfer switch using the NEMA 14-50 output on the Apex 300, which goes to a TT-30 adapter to the transfer switch. The Apex is set for 120VAC mode, because in testing it seems this mode allows the full 30A power on either combination of L1 or L2.

In any case, my question - I have three choices for how to wire the power input to the Apex300:

I’m running the Apex in 30A / 120VAC mode, I’m curious which would be the best option? I don’t quite understand how the power input circuitry works, so I can imagine that 30A @ 120V might be better than 50A @ 240VAC (since that would only be 25A per leg).

Advice?