Can't reserve 100% of mana?

I want to run three 60% mana reserving auras.
I have lvl 19 reduced mana = 72% multiplier
I have Alpha's Howl = 8% reduction.

I have 15% reduced mana reserved from passive (Charisma nodes from ranger cluster)
So total of 15+8=23% reduced reservation.

So total percent of mana reserved is:
180*.72*(1-.23)=99.792%

I'm using blood magic gems so mana doesn't matter.

Why can't I run all three auras???

Honestly probably rounding somewhere in the math. if the reduced mana is actually 72.4% instead of 72% then it ends up with 100.34% instead of 99 and change.

I think it's more like 60*.72*.77 = 33.264 rounded to 34. Do that 3 times and you're at 102.

When you look at the tooltip on your skill bar for one of the 60% auras, does it say 34 in the mana reserved box?

I've counting that percentages in PoE are rounded up, so if it has 1.1% - 1.9% it will incremented up to 2%!

Move the mouse into each gem skill at the skill box and check how much % does the game says. Add each one and you've the reason for why it probably doesn't work.

Coders, usually, round up everything to next int value when they work with values > x.0 so this is probably what they made in here too.