The ratio that i've used all these years has been the same - 1g dmt:1g herb-mix:250-300mg harmala freebase.
At this ratio for me the harmalas don't impart too much onto the dmt experience, though they potentiate/slow of breakdown of dmt to a degree, and imo/ime it's been failproof for me in terms of going deep; could be other factors as well, though contrasting the freebase dmt experience to this changa blend - there's not much difference at all that I can note, aside from the experience being slightly slower [though everybit as intense as fb, if not moreso].
And for a person that doesn't finish the dose in 1-2 big hits typically and takes 3-5 hits - this ratio of harmalas to dmt tends to open up that initial time window of tokes - meaning it extends that initial window of opportunity right in the beginning when you start taking the tokes, so instead of the shorter initial window of freebase dmt you get an extended window due to this ratio of harmalas to dmt.
So 250-300mg harmalas per 1g dmt is what i've always done. A few other members here I know also use this ratio.
Look into 'easy caapi vine alkaloid extraction' by gibran2 for freebase harmalas [you can also use his tek on rue seeds and it works out very well ime].