So, I think we can all agree that efficient shields are probably too good.
That massive pool of shielding makes you virtually immune to bullets for a while (except sniper crits), which makes tacvests less of a good choice. Also energy pistols, electricity, fire. So I had an idea:
What if efficient shields didn't have increased capacity, but instead regenerated energy lost to damage? Like x% of damage lost at y% per round?
So you get shot 3 times this round, for 40, 50, and 30 damage (120 total). You have a strong efficient shield that regenerates 80% of damage lost at 20% of that damage per round, so your shield will regenerate 96 of that damage lost at 19 points per round. Additional damage gets factored in to the total.
High energy efficiency converters exist for energy pistols as well, so we keep them, but they replace shield capacitors for the conservative enhancement (I would make other shields drain 5% of their total each round to make this a better choice). Instead, we let electromagnetic field stabilizers be the "efficient" enhancement component.
I only suggest this changing of components because it makes more sense according to their descriptions, to me anyway.