''Starship Engineering' skills (but only when in space)
Ship type (science > cruiser > escort)
However I'm still not sure how it works. I took a plain Mk1 Shield Array and put it on my Tier 5 ships and found consistent differences between them that I expected. However when I equipped my old light cruiser with the same shields the value was different to my expectation. Additionally, the same shield array on a different character gave a different capacity again.
I think there are more factors than I realise. Does anyone know exactly how to calculate one's shield capacity? Is there a formula?
Are you sure this just isn't the captain skills? Lower tier captain skills count 50% for higher tier ships, but none from the higher ones. So the higher tier ship would have a higher combined captain skill than the lower one.
The Shield Capacity is dependent on the shield and the ship you use first. (I know only specifically that Science VEssel get a bonus to to heir capacity, and Bird of Preys a penalty).
After that, your Captain skills can further improve your capacity. (This is a recent change, I think introduced with Season 2 and/or the RSP nerf). And then there is the new Mark XI very rare console in the Emblem shop that adds +35 % shield capacity.
What I cannot tell you how things stack, or if all bonuses are applied to a base value (and which this would be.)
The biggest factors of shield capacity are the shiled type (Covariant, Resilitent, Deflector, and Regenerative). That determins the base amount of capacity. The next factors is your shield type. Each ship type have a number of modifiers which affects the net values of equipment your equipment on your shield. Shield capacity is among those. Cruisers and similar ships base modifier of 1.0 which you see is what your get when view the equipment poppup info. Escorts and similar shiips have modifiers which reduce shield capacity. (The modifier varies from type to type). Science Vessels have modifiers which increase shield capacity (x1,25 I believe).
Now other factors will increase our ships's net shield capacity (base shield + ship type modifier). I beleive those whay these modifiers work is they are additive with the ship's shield capaicty modifier. The skills which will incrase shield capacity are your Captain Starship (Type) Skills. And the other is the high level Field Generator Engineering Console which is +35% shield strength. Any other shield skills affect either Shield Power Setting Bonuses, addition shield damage resistance and/or the amount of Shield Heals (DoT or Instant) of your Shield Captain/BO abilities.