Siyalatas

Base DPS = 100% = 1		Hero Soul DPS = 10% each = 0.1 each		Siyalatas = 25% each = 0.25 each

Total DPS = (Base + HS) x Siya

10 HS, 5 Siya:
1 + (10 x 0.1 = 1) = 2
2 x (5 x 0.25 + 1 = 2.25) = 4.5

+1 Siya = 6 souls

4 HS, 6 Siya:
1 + (4 x 0.1 = 0.4) = 1.4
1.4 x (6 x 0.25 + 1 = 2.5) = 3.5

At that point, upgrading a level 5 Siya is bad; a 22% decrease.

1,000 HS, 5 Siya:
1 + (1000 x 0.1 = 100) = 101
101 x (5 x 0.25 + 1 = 2.25) = 227.25

+1 Siya = 6 souls

994 HS, 6 Siya:
1 + (994 x 0.1 = 99.4) = 100.4
100.4 x (6 x 0.25 + 1 = 2.5) = 251

At that point, upgrading a level 5 Siya is good; a 10% increase.