Allied units had more teeth than tail than a japanese unit which makes them bulkier to transport especially units returning from the ME or set up to fight a European or Desert War.
I recognize that there was a typo here and that what was meant was that the IJA had more gun carrying guys than an Allied unit of the same size.
BUT, IRL the IJA also was on the verge of running out of ammunition at the conclusion of the Battle of Singapore and very nearly was forced to call off their assault. They had ports and roads but were unable to sustain a typical (read European) scale of combat. They had no way at all to invade India in 1944 without relying on capturing "British" stocks. They got creamed by the Russians when they tried a "stand-up" fight with them. Their logistics systems/units were only partially able to allow them to beat up on the even more poorly supplied Chinese. Seems to me that if they did not win in the "first rush" then they were $crewed to the rail.
Like I mentioned before the (Western) Allied generals were able to substitute bullets/shells for soldiers and the reason for that was that they could get the bullets/shells to the fight in their trucks a lot more efficiently than the Japanese/Axis.
But the only supply effect modeled in AE seems to be that it's harder to get all those trucks onto the beach.







