Well i have just noticed something strange.
On one of my ships I have 6 shields making a total of 68% shield (34% 35% 35% 36% 37% 38%) and i have Shield Master (Increase all fleet shields absorb power) skill up to 6% so this will make a total of 74% shield but my ship have only 72% !
When my skill was on 4% I had the total shield up to 72% and I upgrade it by 2 points expecting that this will change something but it is all the same. All of my ships have the same shield level as they had when my skill was on 4%