Patch 5.4 changed shooting stars' mechanic regarding the chance to proc with multiple targets affected by moonfire or sunfire.
Quote from a blue:
The way this works under the hood is by multiplying the base proc chance by SQRT(x)/x, where x is the number of mobs that have Moonfire or Sunfire active. Note that the proc chances are calculated per spell – Moonfire doesn’t count against Sunfire’s proc chance, or vice versa. So as an example, if the base chance is 30%, and you have Sunfire active on 1 mob but Moonfire active on 3, your Sunfire will have a 30% chance to proc Starsurge on a crit, and your Moonfires will each have a 17% chance.
Source:
http://us.battle.net/wow/en/forum/topic/9653245458#19
'SQRT' means square root. The formula is as follows:
f(x) = 0.30 * x^(1/2) / x
*f(x) is the actual chance for shooting stars to proc off of a moonfire or sunfire crit.
*x is the number of targets affected by moonfire or sunfire.
The chance for each individual dot to proc make your next starsurge instant (from a crit) relative to the number of DoTs active is as follows: (excluding the PvE set bonus and rounded to the nearest hundredth):
1. 30.00% Chance to proc per moonfire DoT. (I.E. 1 moonfire active)
2. 21.21% Chance to proc per moonfire DoT. (I.E. 2 moonfires active)
3. 17.32%
4. 15.00%
5. 13.42%
6. 12.25%
7. 11.34%
8. 10.61%
9. 10.00%
10. 9.49%
