Animals ignore powder of fertility even with 3/4 of aura and only 2 animals in the same chunk.

Yay! I'm glad this was an easy fix. Enjoy :)

How much powder do you have in that stack? The more there is, the bigger the range; you can check with the Mystical Magnifier.

Also, 3/4 of the bar isn't necessarily that much. That's barely enough to get the plant boost effect, so I don't think it's quite enough for the animal breeding effect.

As you can see on the screenshot stack size = 8 and distance to sheeps = 2.
Article "Increase of Fertility" in Patchouli sets requirement 2/3 for Powder of Fertility, and I have 3/4 > 2/3 (aura bar is at left-bottom part of screen).

Yes, but the lower the aura, the lower the chance that it will actually happen, as with all other effects. Have you tried it with more aura in the area?

OK, you are right. I was not patient enough and waited different mechanics. At level 5/6 2 pigs started "work" about once per minute even if breeding cooldown is not passed yet and failed until 5 minutes passed. I waited they will copulate immediately after placement of powder and at end of every 5-minutes period.