Depth Encounters Going Down

I've noticed that the more juiced my maps are, the less I come across the Abysmal depths encounters. I get the chest ones all the time, but not the extra level ones. I've been doing T15s for a few days now I can only remember hitting one or two. I was getting them quite a bit in the 6-12 range. I'm running out of the good mats :)

Its probably just random.
I can get 0 in a day of pure grinding or can get back to back to back.

I went down to T14 to test and see and I get them every few maps. T15? Nadda