Combat, haste, mastery and shadowcraft

[catablitz]

I recently got the cloak in my rogue and as expected I visited shadowcraft to check reforging. (Mind that before the upgrade, my char was allready 'shadowcrafted'). The result though was odd. After hitting auto reforge button I noticed that optimisation included reforging mastery to crit in 4-5 pieces (those pieces were all haste/mastery stat budget) leaving me at 31,5% crit and 34% mastery. Actually I was instructed to reforge +1900 to crit which is almost as much as haste reforged so far. I do love crit as a stat but something seems wrong. I tried to manually reforge back to the rule mastery>crit in those 4-5 pieces and dps went up by almost 125! I also tried mastery>crit with agility gems and went downhill.
So my question is if Fen Yu proc favors so much crit or whether the balance between stats is so ridiculously dynamic. I understand the interaction between stats but why would the spreadsheet advice me to go for crit while I see dps increase -even negligible- when I manually follow the general principle of mastery>haste?

[Dropndestroyrr]

When you hit reforge check the stat weights afterward. Use them to manually reforge afterwards. Shadowcraft does a blind reforge with current stat weights when you click reforge.

[shadowboy]

The cloak proc can crit but does not proc main gauche. As such, the cloak proc increases the value of haste (since it's rppm), and crit (since it can crit), but doesn't change the value of mastery (Since it can't proc main gauche). Same with the legendary meta gem. In a gear set with no legendary meta gem and no legendary cloak, you'd probably see mastery much closer to haste in value.

As an example, with my rogue, with his present gear, EP values are:
(with cloak and gem)
agi: 2.868, haste: 1.519, mastery: 1.295, crit: 1.281

(with just gem, no cloak (by substituting legendary with 2/2 epic cloak)
agi: 2.883, haste:1.537, mastery: 1.384, crit: 1.311

(with agile primal diamond and 608 epic cloak)
agi: 2.939, haste: 1.568, mastery: 1.522, crit: 1.423

Without the legendary meta gem or the cloak, mastery has 97% of the value of haste. With the gem and cloak it's only 85% of the value of haste.

[catablitz]

Thanks guys that makes sense now.