A bit more data; it seems to me that maybe not every K1 nozzle is compatible. Specifically, I tried these “bimetal” (nickel-platted copper, hardened steel tip) nozzles because they had the specs I wanted, but the thread length is just a bit too short. The nozzle bottoms out on the heater block rather than tightening up against the heatbreak. 
Looking more closely, the K1 nozzle you used lists a 15mm length for the threaded portion, which is 0.5mm shorter than the Sovol nozzle (15.5mm thread length), but should be close enough to work. However, the K1 nozzles I tried have a shorter thread (about 14.7mm), which isn’t quite long enough:
I would have tried to screw the heatbreak in a little farther to make up this small difference, but it was locked up with something or another from the factory, and doesn’t want to budge. I didn’t want to break it with too much leverage, so for now I’m considering the K1 nozzles I purchased “incompatible”.
Finally, here are the three nozzle types I tried. I lined them up as best I could. From top to bottom: Polisi3d K1 nozzle (thread 14.7mm, just a bit too short to work), Micro Swiss CM2 volcano nozzle (thread 16mm, installs fine, but shorter overall length leads to suboptimal cooling), stock brass Sovol nozzle (thread 15.5mm):
I don’t really want to buy more nozzles to experiment on right now, but I figured I’d share what I found. For now, I’ll use the CM2 nozzle only for abrasives (and just live with worse overhangs for there), and stick with the stock brass nozzle for normal prints. (And maybe I can return the K1 nozzles as I wasn’t able to use them…)
That said, if someone is able to remix a slightly shorter fan duct, then I think most any volcano nozzle would work well. (Sadly that’s outside my skillset today, but maybe someday!)