Arcane surge bug or that supposed to be like that?

For the past few days i'm trying to make DPS/damage calculator for my spark. I polished it to very accurate numbers, but the main issue is automatically getting cast speed by given tree increases and items i have, but then final test for me is Arcane Surge buff thats increases my cast speed by max mana.

This is how i'm calculating it right now, but increases and downcreases changes that accuracy i have with my numbers (now it gives me output ~0.1 vs the game):

How do i calculate my mana:
(raw mana, eldrich battery)
30 = base mana
92 = level
272 = intelligence
20 raw mana from tree
1597 = energy shield from items
1396 = mana from items

(30 + (92 * 4) + (272 * 2) + 20 + 1597 + 1396) = 3955

Mana with tree/items increases:
3955 * 1.33 (33% increased) = 5260 (same number that is in game)

How do i calculate how much arcane surge adds up:
10 = base cast speed
3955 = raw mana
1.153 = square root of 33% (1.33) mana increases
0.7 = arcane surge increase from tree

1 + (10 * (5260 / 15 / 100) + 0.7 + 1) / 100 = 1.52 times
1 + (10 * (3955 * 1.153 / 15 / 100) + 0.7 + 1) / 100 = 1.47 times
1 + (10 * (3955 / 15 / 100) + 0.7 + 1) / 100 = 1.43 times

How do i calculate how many casts per second i have:
0.7 = spark cast time
62 = cast speed increase from tree
43 = cast speed increase from items
1.52 = arcane surge increase 1
1.47 = arcane surge increase 2
1.43 = arcane surge increase 3
1.25 = spark support that gives more cast speed by 25%

(1) 1/0.7 * (1 + 0.62 + 0.43) * 1.52 * 1.25 = 5.56 times per second
(2) 1/0.7 * (1 + 0.62 + 0.43) * 1.47 * 1.25 = 5.38 times per second
(3) 1/0.7 * (1 + 0.62 + 0.43) * 1.43 * 1.25 = 5.23 times per second

and my cast speed (5.41) is very close to the second output above.
its seems that arcane surge does take all increases on mana but at the same time it does not. More increases/downscreases on mana changes accuracy with second method.

Im looking for some ideas, maybe someone already got that formula im looking for. Lets discuss.