The active ability on phalanx deals damage to units trampling over it. The amount is shown as 300 on U3 on the tooltip of the card, while it shows 270 on the icon on the card when the ability is active.
I think the reason for this is so the soulhunter can use its minefield immeadiatly. Normally the soulhunter will attack you until he sucked up a certain amount of corpses, after which he will place his minefield. If you go to him, you will notice him using his minefield immediatly, which is supposed to make this part a little more difficult.
Makes sense.
Lvl 10 is already hard enough for many players and the time doesn't really help with that.
There is in general very little reason on why you have ~40 in 1p, ~30 in 2p and ~2 in 4p or at least I didn't see it.