Would be better to base the increase on focus. Possibly have the value equal to cast cost plus skill level as a % of focus. I.e. skill at 20/25 equals a plus 20% of focus. This would be at max ability level of course. At least then there would be some scaling with focus but still give a decent base for mages that don't max our their focus/energy.
I dont think that would work either.
Lets start from scratch. We want a skill that turns energy into a force field of hit points to absorb damage.
I do like using percentages because it does not matter what level you are you can always calculate a %.
I would make it based on total energy instead of focus because items and spells like energy well give extra energy.
How much? This depends on our design constraints. There appears to be a theme with the update that the devs want us avoid just maxing out our favorite abilities. They want us to be more thoughtful about choosing our levels. So lets make the max shield something that would off balance our character, say it was like before the update of full energy. If someone wants to be a mage tank and max it out, why not.
And to do that you would need to max out everything to get there, skill points, and ice ability.
So lets just go with pure percentages and see what it looks like.
Shield Str = Max Energy * (Ice Ability/ice abilty max) * (skill points / Skill Points max)
so how does this work, assume 95% of ability is trained
Low level with 5/10 875 E = 415 shield
Med level with 2/15 1800 E = 228 shield
Med level with 15/15 1800 E = 1710 shield
High level with 20/25 3000 E = 2280 shield
High level with 5/25 3000 E = 570 shield
So how much energy should it cost?
If we are using up our energy 1-1 then you might as well make it a fast refresh since our energy is the limiting factor like it was before the update.
If they are going to keep the very long recharge then we should get 2 to 1 to make it more comparable to heals.