It could also be that the elementals cause lots of damage all around, and when the one or two guys die, the others are already badly wounded and total damage exceeds 75% of the total starting hps.
Nah, as I said, this happens a lot to me a team of morale 17-19 blessed sacreds defending, 2 gets crushed, maybe 3 if i'm lucky before they route auto-routing the commander. I think two bodyguards is the way to go.