@exselsior
Based on looking at the blueprints as well as the cumulative upgrade costs in game, it appears that the following is the cybran shield hp per mass:
ED1: 4000/160=25
ED2: 7000/460=~15.22
ED3: 10000/1260=~7.94
ED4: 13000/2460=~5.28
ED5: 16500/4260=~3.87
So, ED1 is quite mass efficient, ED2 is mediocre, and the rest are quite inefficient, but the trend in efficiency is comparable to the tech-equivalent shields in the other factions (T3 is much less mass efficient than T2, ie: sera T3 shield hp/mass is ~5.83), but with ED1 and ED5 as more extreme.
TBH, I feel like a reasonable argument could be made that T3 shields are too expensive compared to T2 shields.
@ZetRoy
You are focusing too much on shield size. Shield size is not as important as shield hp per mass.