The effect only applies to Max HP buffs, which means Virtue and Temperance, but also your HP Type One and self Shielding buffs. So anything listed under HP Buffs (including all Aegolism spells) will be extended 30% over any AA you have for a new max of 80%
I realize this is 2 years later, but better late than never.
4: Limit: Effect(Max Hitpoints Allowed)
This Focus effect is limited to only those buffs that increase maximum hit points. Such as the Aegolism and Symbol lines, as well as the self-only Shielding line.
This effect will not work on heal-over-time spells, as these spells have no effect whatsoever on your "maximum hitpoints"; they only increase your current hit points by the given amount per tick, up to your current maximum.
Think this only applies to extending buffs not HoTs due to Line 4 as a previous poster said. Something like the a Drape of the Unending gives 20% extension to HoTs.
WOW, 30% extension, and 24 sec min duration, which means this should add to HoT and death save spells (assuming the limit on line 4 doesn't block those).
Either way, this would still leave you with 80% extended buffs (50% from aa + 30%), which is incredible.