Rune of the Pack not affecting animal companions when initiating combat using an Engage skill

I'm trying it out in a new build, and I've noticed that it doesn't seem to affect the animal companion when you land the first blow off things like the raptor and gryphon. I've not tested the skyscale but I suspect that it's fine due to the mechanics.Taking an educated guess, I think it's because the boons are being applied before the animal companion is spawning in. I've tried the raptor's tail-sweep on several mobs and the while I have the boons, the animal companion always has nothing. This is supported by the fact my ranger build's got Nature Magic (and so boons appplied to me go onto the pet): if the pet isn't there then it won't get any boons off me either, which is consistent with it being boonless after the tail-sweep.