'bout the base shield--how about it degrades by % of its health every X seconds?
So, say, every 5 seconds 1/4 of the shield is gone...it self adjusts to higher shields, which become a less effective investment as the shield loses more health per 5 seconds.
Just an example, but IMO a little simpler than setting a flat value and increasing for each chunk of shield HP.
Good point Destroyer. Good point. It looks like the only solution to the deserter problem is to tell your partner to stay in the game, and hope that he/she will stay in it. Lol.