Arelith

Please change the concentration check formula to avoid casting failure to something that's more easily passable, like:

15 + spell level + damage received / 5

The current formula (10 + damage received + spell level) often results in unpassable (DC127+) checks and can lead to very high DC (80+) checks even after regular (non-critical) hits.

The ask on the player here is pretty much to prevent their character from getting damaged at all.
While careful positioning might do the trick in PvE, it's not a reasonable ask during PvP encounters.

Furthermore, if the premise for instant death DC spells being unreliable because they're unfun applies, same principle should be observed here here - concentration check failure is very oppressive and unfun when it happens.