Not sure if this is intentional, but increase/decrease application of HP is applied before blood magic. This makes % change less significant for those who pool points into MP or just into power, which is great for my build due to decreases applied by glasscannon/empower, but probably terrible for those who pool points into MP on the wizard.
That’s intentional, at least… stacking health reduction to gain power and Blood Magic to gain power weren’t really meant to co-exist well together. If you’re making that a viable build though, I’d be impressed! 