Panzer Campaigns - Road Stacking

[BigDuke66]

Hi
From the manuals description it should be obvious how the road stacking works but what I see in the game is a bit different.
I'm fooling around with France 40 and Alt scenarios of Volcano Man, the road stacking here is 350 so I expected to break my battalions down to companies to be within that limit to benefit from the road, but now I see that also a single battalion can move by road and benefit from that road movement but these full battalions are close to 600 men strong.
So I guess what the manual tells is not the whole tale, anyone here can explain how it works?