Tooltip says 50% of the amount of HP. Right. In the overland content, the shield is exactly half of my hp, regardless of my magicka values. No problems.
When I enter Cyrodiil, battle spirit says 5k is added to hp but 50% of shield is reduced. However, no matter how I try to calculate I cannot get my current shield value.
The trouble is, magicka values go into that calculation. If I slot, for example, Bound Aegis with 8% magicka, my shield goes up almost 1k. If I do the same in overland content, shield does not change. Paradoxically, if I use tri-stat glyph to up the HP for 570, I get less shield in PVP than using pure magicka glyph on that armour (because with tri-stat glyph you get 50% less magicka).
So basically magicka>hp for shields in pvp.
What's going on here?