mass prospect drop chance issues

[vladoo]

WoW Freakz link: https://www.wow-freakz.com/item_finder.php?item=123919&&name=felslate
Bug description:
Based on the drop chances mentioned on the freakz site, while prospecting felslate, for every normal prospect (5 felslate):

- there's a 20% chance to get from each uncommon gem type 2-5 pieces. Assuming a normal distribution between 2 and 5, that means 3.5 pieces, we get a total number of 3.5 x 0.2 chance x 6 types = 4.2 uncommon gems per 5 prospected felslates.

- there's a 16.67% chance to get from each gem chip type 1 piece. Considering they all convert to grey gem chip, that's basically 1 gem chip per 5 prospected felslates.

- there's a 5% chance to get from each rare gem type 1 piece, so basically we get a total number of 0.05 chance x 6 types = 0.3 rare gems per prospect.

I tested mass prospect for felslate using a sample of 5200 felslate (1040 x 5). After mass prospecting them (260 mass prospects), I obtained a total number of:
- 1325 uncommon gems
- 1031 gem chips
- 30 rare gems

Considering the above mentioned drop chances, I expected:
- 1040 x 4.2 = 4368 uncommon gems. The actual number of dropped uncommon gems is around 30% of the expected outcome.
- 1040 x 1 = 1040 gem chips. The actual number of dropped gem chips is 99.32% of the expected outcome.
- 1040 x 0.3 = 312 rare gems. The actual number of dropped gems is 9.61% of the expected outcome.

From my calculations:
- rare gems drop roughly 10 times lower than expected
- uncommon gems drop roughly 3.5 times lower than expected. This seems interesting, taking into account that those drop rates are for 2 to 5 gems (3.5 on average). It seems that the drop chances are actually for 1 uncommon gem.
- gem chips seem to drop predictable

Below there are two screenshots proving the prospecting of 5200 felslate, and on the tinyupload link there's a spreadsheet detailing the above calculations overall and broken down per gem colors.

I don't know if I can replicate these results using the basic prospecting of a 5 felslate stack, so I don't know if there's an issue with prospecting in general or with mass prospect, but the actual drop chances for uncommon and rare gems seem to be way too low, in my opinion. The only item which drops spot on seems to be the gem chip.

Proof: https://imgur.com/a/rrXegFs
http://s000.tinyupload.com/index.php?file_id=45484316523505149661