High quality circular wave amplifiers absolutely destroy the capacity of shields, often to the point where the capacity is actually lower than some of the thresholds. For example you can end up with a shield that has 250 threshold against very high speed attacks but only 200 capacity, so it won't be able to soak more than 200 damage from a single attack.
As such it's a better idea to use one with lower quality, so you end up with a shield that has enough capacity to make use of those higher thresholds. Efficent shields are better 99% of the time, but amplified double high frequency shield can be a life saver against snipers, especially for squishy builds.