CS2 results vary?

[mbncd]

I've usually found CS2 (Careful Synthesis II) results to be fairly uniform. They may vary from recipe to recipe, giving more or less progress depending on the difficulty of the item being made, but within the same recipe they're usually pretty uniform.

Because of this, I've taken to finding out how much progress I need to finish high difficulty items with one last CS2 and gotten the progress up to within that range before trying to work on quality. This allows for unlucky runs with good/excellent statuses just not coming my way when I really need them to, thus I never break an item, which has been a problem when I haven't prepared in this way.

Yet, I've found that sometimes my CS2 gives more progress than it did a step or two before and I'm unintentionally finishing a craft when there should have been a little progress left.

Take for instance, this pair of gloves I was making:

[18:49]You begin synthesizing a pair of serpentskin gloves of casting.
[18:49]You remove the following from your bag:
[18:49]2 earth clusters
[18:49]1 wind cluster
[18:49]2 circles of amphiptere leather
[18:49]1 spindle of crawler silk
[18:49]1 hardsilver ingot
[18:49]1 bottle of grade 1 intelligence dissolvent
[18:49]  You gain the effect of Collectable Synthesis.
[18:49]  You gain the effect of Comfort Zone.
[18:49]You gain the effect of Whistle.
[18:49]You use Whistle While You Work  Success!
[18:49]  You gain the effect of Inner Quiet.
[18:49]You use Tricks of the Trade  Success!
[18:49]  20 CP recovered.
[18:49]  You gain the effect of Ingenuity II.
[18:49]You use Careful Synthesis II  Success!
[18:49]  Progress increases by 219.
[18:49]  Durability decreases by 10.
[18:49]You use Careful Synthesis II  Success!
[18:49]  Progress increases by 219.
[18:49]  Durability decreases by 10.
[18:49]You use Tricks of the Trade  Success!
[18:49]  20 CP recovered.
[18:49]You use Careful Synthesis II  Success!
[18:49]  Progress increases by 310.
[18:49]  Durability decreases by 10.
[18:49]You use Careful Synthesis II  Success!
[18:49]  Progress increases by 310.
[18:49]  Durability decreases by 10.
[18:49]The pair of serpentskin gloves of casting is added to your inventory.
[18:49]You synthesize a pair of serpentskin gloves of casting.

I wasn't paying attention, clearly, or I would have noticed that the results of the CS2 had gone up from the 219 the first couple of times to 310 the last couple of times. I was thinking that as it was 219 each time I could just do it 4 times and it wouldn't finish.

Why is this? Is it something to do with Whistling or Tricks of the Trade or the fact that I got a good status? I'd really love to learn the logic behind what's happening here.

[Grotesque]

Whistle at 9,6,3 stacks gives you +50% progress bonus.

[mbncd]

Whistle at 9,6,3 stacks gives you +50% progress bonus.

Ah, that solves it! Thank you very much!