Increased duration (support) with immortals call

i have noticed that when you combine these gems together the extended duration only applies to the initial 0.20 seconds. The support gem has no effect on the largest feature of immortal's call which is the duration per endurance charge. Thus rendering the gem totally useless.

Is this meant to be? or is the duration per endurance charge meant to be extended.

(p.s. im kind of disappointed as i tailored my build towards making this combo)

no 1 has their opinions on this?