Torment scarab of possession not working correctly when using 4

Taken from PoeWiki (and the fact that you can add 4 scarabs, intuitively):

"

Using multiple scarabs will increase the chance but not the number of Tormented Spirits possessing a monster.

Repro steps:

1. Open map device
2. Add 4x torment scarab of possession in 4 empty slots
3. Add map


Expected result:

All rare monsters being possessed by at least 1 tormented spirit.


Actual result:

Most rares not possessed.


Screenshots:

Scarabs in device:


First rare encountered: (Yes, I died for this screenshot)

Bump. I also experienced this.

A similar issue exists for Torment Scarab, which states "Tormented Spirits in Area have a 25% chance to be set free when Possessed Monsters are slain".

Stacking 4 of these does not guarantee that the Tormented Spirit will escape.

This might or might not be a bug.

The scarab states that rare monsters in the area have a quarter chance to be possessed by up to 1 tormented spirit...confusing terminology, yes.

Assuming "up to 1" translates to "a maximum of 1" (because 0 technically qualifies as "up to 1"), the "quarter chance" could be interpreted in either of 2 ways:

1) Each "quarter chance" (25% chance) stacks additively and the check is made a single time, suggesting that 4 stacked scarabs provides a 100% chance for each rare monster in the area to be possessed by a single tormented spirit.

2) Each "quarter chance" (25% chance) is checked independently (sequentially), and this interpretation is more consistent with the mod itself (up to 1), because if either the rare monster was already possessed without this scarab mechanic, or if the 25% chance was satisfied multiple times by successful sequential rolls of multiple scarabs for a single rare monster, the mod limits its application (possession of the monster) to situations wherein that rare monster has not already become possessed through some other mechanic or by a previous successful roll in the chain.

In Case 2, the actual chance for a rare monster to become possessed, in the presence of 4 scarabs, is 68.359375%, which is 1-(0.75^4), so only about 7 out of 10 unpossessed rare monsters would become possessed through agency of the scarabs. Case 2 is probably the way in which the scarab actually functions, which would imply diminishing returns for increasing numbers of scarabs.

To expand on the above, the actual chance of N scarabs to cause an unpossessed rare monster to be possessed would be:

N = 1; 1 - (0.75^1); 25% chance for 1 scarab
N = 2; 1 - (0.75^2); 43.75% chance 2 scarabs
N = 3; 1 - (0.75^3); 57.8125% chance for 3 scarabs
N = 4; 1 - (0.75^4); 68.359375% chance for 4 scarabs

The 2nd scarab gives an extra 18.75%, the 3rd gives ~14%, and the 4th a measly ~10.5%.

By the way, the same logic might also apply to the Torment Scarab, but that scarab is limited to 2 applications, so it would be an exhaustive project to gather the data and be sure whether it was happening 50% or 43.75% of the time.