What would be your goals with this caapi extraction? Presumably - and in keeping with this thread - you'd be focussed on getting a usable tincture with a favourable ratio of harmala alks to ethanol. You don't really want to be getting blind drunk in the process of consuming an adequate dose of harmalas, after all!
The probable reasons for the lack of information on (hydro)ethanolic banisteriopsis extract are essentially twofold: firstly, the low concentration of alkaloids in the plant material entail an inconveniently large volume of solvent; and secondly, the harmala alkaloids have fairly poor solubility in ethanol, again forcing a larger than optimal volume of solvent.
Your best bets may be either to make a concentrated aqueous extract to which you can add ethanol as a preservative, or to use a low proof spirit (say, diluted vodka) for the tincturing process. It would need to be at least 18% ABV to prevent acetous spoilage, and I'd suggest an absolute maximum of 30% ABV.
It's rather easier to make a tincture of rue seeds since their alkaloid content is so much higher, as well as being concentrated in the seed coat.
One further option is to do an ordinary extraction on the caapi and then see how well that dissolves in alcohol of various strengths. You'll probably have to way attention to the particular salt forms as well, and be aware that, given the freebase forms will barely dissolve in neutral water, some experimentation will be required. And once you've come that far, you may as well consider dispensing with the ethanol entirely and going with an oxymel approach:
