Man that's a great picture
In the SM's case, that is a much smaller motor with lower pressures, but it's operating in the vacuum of space where ambient pressure is essentially 0
If that engine were to fire at sea level, the resultant low pressure inside the bell, and the 14.7 psi outside would give you something closer to Krushnic, but would probably Krush the nozzle in! It's an extreme case of (a) in the image below)
Think of the Falcon 9's Merlin engines. there are 9 on the 1st stage and their bells are ~3.5 feet across (that number may be off, it's been awhile). They operate within the atmosphere and are optimized for lower altitude, and as you watch the video, you can see the radiating exhaust plumes as atmos pressure lowers and the exhaust gas expands (case (c) below)
On the 2nd stage, there is a single Merlin-Vacuum engine which is basically the same combustion chamber, with mostly similar plumbing, same fuel, but a big
9' nozzle extension on it! It operates in the very high atmosphere and vacuum of space and requires the much larger expansion ratio. (if you fired the M-vac at sea level with the skirt on......you would have a very bad day)