Alkaloid contents in ayahuasca are extremely variable between preparations and batches. Specially in the area of betacarbolines, that have variable contents themselves between harmine, harmaline and THH.

I wouldn't take one sole study as reference to prepare what works for you. If you want to use studies to calibrate dosage, look at several of them and calculate medians. I'm leaving attached another paper that reports concentration levels from several reference samples, and as you will see they are mostly higher than the one you mention. In all of them, the amount of betacarbolines per ml is higher than the amount of dmt per ml, often significantly higher.

And regarding your psychotria harvest routine... have you analyzed samples extracted at different day times? Not that the yield you report sounds low, but dmt is reported to be found in other botanicals (the clearest example Phalaris spp.) in higher amounts at dawn, after the dark period of plant metabolism.