This is awfully small when folded
Yes, pretty compact (especially if that's the 6.5x9 model). Kalart rangefinders are sometimes found on these old plate cameras, even these little ones, but at best they're a little bigger than a Bessa II or Moskva 5, and the one pictured lacks the rangefinder feature.
A Barnack Leica is one reasonable choice for very small rangefinder camera; a Contax II isn't much bigger (but apparently much harder/more expensive to get serviced). Can't say I've handled a Leica of any version, so I can't verify the size, but it would have to be pretty small to beat out my Welta Weltini or the very comparable Super Jubilette, Super Baldinette, and other pre-Retina 35 mm RF folders.
A 127 half-frame (3x4 cm) folder with rangefinder would likely beat all the 35mm RF folders, but I've never seen one that I recall, and haven't been able to quickly confirm that such a thing ever existed. Kodak/Nagel Volenda is where I would have expected it if they were ever sold, but I don't believe they were. I suggest this because my Baby Ikonta is the same size or smaller than my Rollei 35, so adding a rangefinder would still leave a camera in the same size range as an Olympus XA or Weltini. Historically, 35mm had beaten 127 for anything above "two Christmases on one roll" family pictures before rangefinders found their way into the lower price ranges (where 127 cameras hung out after the VPK derivatives were discontinued in 1936), and the 127 "comeback" of the 1950s was mostly in square format (and I don't recall seeing any of those with an RF, either, though there were a few pretty good TLRs). And for "really small" the Bantam Special was the only folder with RF that beat out the Retina for size and weight after WWII -- and it took 828.
Mind you, those were really good cameras, with the best lenses Kodak offered at the time, and pretty small -- but 828 isn't even semi-available any more the way 127 is, and was never as popular as 127 in the first place (tiny roll film was harder to load than 35 mm, hence why 126 came along to replace it with drop-in loading). If you don't mind recutting and respooling to turn 120 into 828 (you'll get 16 on a roll with suitable trimming of the paper leader and tail, 28x40 mm image area), or recycling backing paper with 35 mm film rolled in (giving 8 or 12 on a roll, depending on the backing you get) a Bantam Special is a compact and convenient camera to pocket. Decades expired 828 film isn't hard to find on eBay (albeit at collector prices) to supply spools and the tiny metal cans Kodak used to protect the film rolls.
