Barrier counts your resistances / ignite ignores resistances.. since it is true damage.
Don't use barrier to block ignite, use barrier to block their actual non-true damage and you will have the hp to survive ignite.
Just make sure they don't penetrate ALL of your resistance and have 1 cloth armor or 1 null magic robe or whatever...that way you have more effective hp.
Barrier in most situations is actually stronger than ignite but it never directly counters ignite.
So the more resistances you have the more effective hp that shield gives, but ya ignite is true damage so stop trying to barrier the ignite..especially when it outlasts barrier.