So first off I'm in a similar boat to you.
I'm yet to break through with changa and with DMT (the changa is more out of my own doing because for some reason have some hesitancy around it, honestly can't put my finger on it as I've had no issues with LSD and Shrooms going balls deep haha, but I know that when I do decide I'm ready to breakthrough it will be a wonderful experience and hopefully grow me as person).
But yes I've done low doses of both and I can see why the low doses of both can be somewhat uncomfortable, I'd best put it as taking a low dose of LSD and not quite tripping if that makes sense?
It's still pleasant but somewhat aggravating in the sense that you're still in control and therefore I feel like my being is somewhat trying to fight it whereas if you breakthrough you don't really have the option and will just take the experience for what it is.
On the flip side I've found smoking very small quantities of changa and I mean like one toke maybe two is very pleasant brings a nice buzz for 30 minutes or so but all in all I wouldn't say it's worth the use of the changa in this way.
In terms of smoking it in small quantities I would use a pipe not a joint.
One because I've read quite a lot that mixing cannabis and changa can be unnecessary overwhelming and a lot on your heart, I also imagine that the cannabis won't add to the experience particularly if anything alter what changa is all about although I imagine these things are purely subjective.
And secondly using a pipe is very very easy to control how much you take.
Hope that this helps and hope that you have an excellent time with it, let us know how it goes