That's no doubt the DMT N-Oxide in it that you are feeling. DMT N-Oxide has slightly different effects from DMT. It is milder and SWIM finds it more pleasant than DMT. Psychotria, being a leafy material, contains a lot of its DMT in the form of DMT N-Oxide. Leaves generate oxygen and so the DMT in the leaves being surrounded by oxygen is very likely to oxidize into DMT N-Oxide.

DMT N-Oxide has a slightly slower onset, slightly longer peak, and slightly longer overall duration. It’s water soluble while DMT is practically insoluble in water. DMT N-Oxide is more relaxed, less speedy, and less "psychedelic" while remaining very visual. DMT N-Oxde is the form of DMT most often found in Yopo and Vilca (along with higher amounts of 5-HO-DMT and 5-HO-DMT N-Oxide usually).

I believe the primary reason that people find ayahuasca made with psychotria more mellow is because it contains more DMT N-Oxide than Mimosa hostilis usually does.