Question about fire skills

I'm playing through my first character and I've just ascended. Had a few questions about some of the skills.

Immolate has been a favorite (among others) to pair with Flare and Fireball in taking out single enemies. But then I get Incendiary Bonds. More damage than Imm., 3 sec delay, aoe. But more cost and longer recharge.

I've noticed that IB doesn't always seem to set the enemies right next to my target on fire, or do the initial damage, consistently. Also, it doesn't always seem to last 3 seconds. And, it seems that if the monsters run away from the target and his area after it has been cast, they stop burning prematurely.

Am I not seeing it correctly?, or is this spell sometimes bugged? Maybe the AOE is just really small? Does it actually function like a flame trap, in that if you run out of the area you stop burning? I've been so frustrated that I've stopped using it and have just gone back to Immolate.
Thanks

another fun thing is use IB then cast fireball..FB reaches target around the same time IB goes off and you can surprise the enemy with a good dose of damage..follow that up with IMMO and the target should be close to dead..


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