Having a separate barrier bar, or always having the barrier bar start from 0 rather than appending it to the end of actualHP, is less readable than appending it to the end of actualHP. For example, if you have
- a DD at 15% aHP with 15% barrier
- a DD at 10% aHP with 20% barrier
- a DD at 25% aHP with no barrier
and you know an AoE is coming up that that deals around 25% HP raidwide damage, which DD is in the worst position?
If you append the barrier bar to the end of the aHP bar, then it's easier to read who has a higher effectiveHP at any given moment.