there are 2 considerations:
- fit
- weight displacement
when it comes to fit, here is the bad news for you: there’s been a move toward, not away, from a consensus geometry. for me (for example) it’s a frame stack of 540mm and a frame reach of about 425mm. what is not uniform is what that bike size is called. it’s either a 54cm, a 56cm, a M or an L. all those are used by various brands for that size. but there’s not a lot of bikes lower than that 540mm stack, for a guy 6’ to 6’2".
the happy news is that the frame geometry is not really that big a deal, because there’s way, way more variance in how the aerobars adjust. your options occur inside of a rectangle or parallelogram for every size. the “sides” of that rectangle are how close in, and how stretched out, that bike will adjust for you, and the top and bottom of the rectangle is how low and how high the bike will adjust. what you are looking for is a bike that has the bottom of the rectangle low enough so that your armrest position is available. you might have 2 bikes built on a chassis that i just described, 540mm x 425mm, and one might have the lowest available pad height at 625mm and another may go down to 575mm, because it’s got a front end designed to go quite low. so, don’t look first at frame geometry. look at the rectangle (or parallelogram) and see if you can not only go down low enough, but that you get there somewhere close to midway between the near and far vertical sides of the parallelogram.
then there’s weight displacement, front to rear. if you get a really small bike, so that you can get low enough, that bike might not have a very good weight displacement. for example, BB to front wheel axle - called front center - i want a certain distance there. not too short, not too long. i don’t want to ride a unicycle, and i don’t want to ride a tractor trailer. a front center between 610mm at the shortest, 635mm at the longest, that sits the front wheel underneath me pretty well.
you shouldn’t have trouble finding what you want. ask LAI on the forum. he’s got a really low position. also, cyclenutnz has some of these parallelograms he can show you, that shoe the available sizing options, both with profile design bars (like the subsonic) and for bikes that make their own bars.
but in general, a canyon speedmax CF, with a subsonic, that is a low bike. that’s the entry level bike, and the new disc brake and old rim brake both have the subsonic. there are issues with adjusting the subsonic on that bike we can talk about, but that’s a long-low geometry bike with a low-position aerobar, and i suspect that bike - if they have any in stock - is a real deal right now, if you get the rim brake version.