Ahh... Instead of doing a kilo at a time, it's way easier to work with 100 - 400g of bark at a time.
When doing a STB, you really need a 1:1 ratio of bark and lye to get all of the goodies out. A buddy of mine uses 250g of bark and 265g of lye and gets awesome yields of really orange, oily stuff. When he uses a 1:1 ratio the end product is more of a yellow instead of orange.
If you were to switch to an A/B you could use a lot less lye but you'd also get a lot less from your xylene pulls.
I'd really recommend instead of experimenting with large extractions, do several different 100g extractions and find what works best for you. Then scale it up once you have it down.
Convert a melodic element into a rhythmic element...