I'm in the same basic climate as you and do some treestand sitting about half the time. I can not stand cold or bulk and have spent quite a bit of effort trying to figure out what keeps me warm without feeling bulky and heavy.
I got the Pnuma heated layers and wear them next to skin along with some heated socks. I wear a very light mid layer over those if its at the bottom end of temp range. I wear the Stratus down to about 40 degrees. Any lower than that, I get into the Fanatic. If you minimize mid layers, it isnt too bulky. I add in a neck gaiter and good hat (game changer) and I'm good to go for sitting.
It looks like you're already pretty packed into that Stratus with all the layers. The Pnuma was pricey but completely worth it and negates the extra layers. The Fanatic won't be anymore bulky than what you are already wearing.