Well, what if you spam HL, then you wouldn't get that full 44 mana if my understanding of the libram is correct, unless it stacks.
For example, with the numbers on the left representing seconds:
0 +0 mana, Start casting HL...
1
2
2.5 You cast HL, you gain 22mp5 for 10 seconds, start casting next HL
3
4
4.5 You cast HL, you gain 22mp5 for 10 seconds (refresh timer), start casting next HL
5 +22 mana
6
6.5 You cast HL, you gain 22mp5 for 10 seconds (refresh timer), start casting next HL
7
8
9
10 +22 mana
11
12
13
14
15 +22 mana
16
16.5 timer ends
66 mana gained with 3 HL casts.
So now you only got 22 less mana per HL, not 44.
If it stacks and refreshes though then you can get a ton of mp5 by spamming HL, though you would lose mana FAST so its not really viable to do that.