Mines?

[seabolt]

I'm 100% sure that in H2H I can see how many mines my minefields have, (1) means that my engineers have been able to lay one mine to the hex. Icon tells both sides if it has 10 or 20 or etc up to 50 after which the icon shows five mines.

In H2H, yes. In SPWW2 the defender can only approximate that there's 4 to 10 (IIRC) mines per icon. The latter creates a large difference in practice:

SPWAW and H2H: Mine tally drops from 10 to 7. Drop every artillery tube you have behind it at 0.4 delay and decimate the attacking force.

SPWW2: Mine tally is somewhere between 4 to 10 mines. Mine icon disappears. Drop every artillery tube you have behind it at 2.4 delay. Wave bye-bye to the untouched attacking force that's already threaded the breach.

The former allows you to screen large stretches of front with a single row of mines. The latter requires at least double the investment for the same purpose (so that the defender can see the second mine icon disappear), and with SPWW2 engineer clearance rates that still may give you only a single turn.

EDIT: Fixed acronym dyslexia. Maybe.