The cone is pretty much a deceiving visualization due to how MGs actually behave. No Axis MG can actually cover it's cone of fire, whereas the maxim's cone is a more accurate representation of what ALL the mg's actually do ingame. For the most part, only the dotted line with the arrow matters.
Did you know that you can manually target squads with MGs when they are set-up? Honest question. Also take a look at the veterancy for MGs:
Vet 2 +20% Suppression +30% Horizontal Traverse
Vet 3 +20% ROF +30% Accuracy +10% Horizontal Traverse
all dat horizontal traverse.
Also, the vet 1 mg42 ability is pretty much a free 'advance on this mg position' anytime it's used because the mg has to do the full reload animation before firing which takes like ten seconds. It makes sense at first, but to use it effectively you have to preemptively use it a few seconds before the enemy begins its advance, else you waste munis and watch the timer tick down.
That is why you suppress first then activate Incendiary Rounds. The ability is fantastic (and there is a 10% faster reload bulletin)