Does heroic farming and compass prevent you from getting t1-2 only, or does it improve each resource you pull buy 1-2. Like without compass and heroic you get a t10. would that be a t12 if you had heroic and compass?

if you find a t28, in heroic or just compass it would have been a t29, with both a t30. each does add +1 to whatever base tier you find, thats why it eliminates t1/2

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Computing the probability that at least one of the following events will occur:
P(a or b ... or z) = 1 - P(!a and !b ... and !z) Probability

The only exception I have found is if you have zero (0) skill in a resource and then you will get T1 resources even if you have the compass and use hero mode. But once you have 1 point in a skill then it works as expected and the lowest you will find is T3.