I played an interesting game. I was undead and had some archers in a central wooded area who were mostly ignored for a time. As my army started talking to pieces I had to make some interesting choices in target selection as I was fighting to keep my opponents score down.
Because trays cost less the bigger the unit you also are loosing fewer points at first. Let's take an example of the reanimates. At 12 trays they are maxed. If you lose 1 tray then you only score the points for a 9 tray unit. After that you can lose 2 more trays with score loss on the 3rd. Followed by 2 more safe casualties with a bigger score loss on the 3rd. Followed by one safe then a point loss etc.
So the smaller the units get the more points casualties cost you and the faster you lose those points. Once you are down to a 2 tray unit any tray loss negates your points unless it is a siege piece. Could be a balance to msu armies. It's late so I hope I am explaining my thoughts correctly.