Fissure doesn't seem to do anything. I went to a bunch of rooms with different mana and tested the impact of charging an orb with and without a ETF in the room. I was able to measure an increase from increasing room mana, but it was the same before and after the fissure was cast.

ETF details:
spell stance 100 100 100
min prep with 10 mana harnessed
Cast fire
makes a small fissure that adds a decent amount of extra elemental energy for 15 mins.

attunement remaining after charging 50: before and after casting ETF

before	after
pale 7/21	pulsating 10/21
45%	45%
flickering 8/21	glowing 11/21
48%	48%
shimmering 9/21	lambent 12/21
49%	49%
pulsating 10/21	shining 13/21
53%	53%
glowing 11/21	luminous 14/21
54%	54%
lambent 12/21	radiant 15/21
55%	55%

That's not what I mean: even though it elevates the amount perceived in the room, the amount of attunement that I use doesn't change to what it would be in a room with that higher mana.

In a room that I perceive to have pulsating mana, charging 50 mana into an orb costs 47% of my attunement.

In a room that I perceive to have pulsating mana after casting ETF in it, charging 50 mana into an orb costs 55% of my attunement; the same that it costs in a room with pale mana.

It's not that the spell doesn't add enough to how much I perceive, it's that the extra mana doesn't actually impact how much attunement that is used.