Thanks, I suspected as much. I'll get something with lower RDSon (not sure if I should go bigger package than TO252, probably not), step the sense resistor up to 3W version, and get a bigger inductor. The evalboard recommended inductor (Wurth 744771133) is also only ~3A rated but IPK(cs) according to power&compensation spreadsheet is 4.15A.
Unfortunately 12V is non-negotiable in my setup, so I'll have to deal with it.
Still, I'd like to know the thermals of the 5211-EVAL while running with the led board that it comes with - 4 strings @ 100mA which should be a fairly similar setup. I guess it's probably capable of running off a 24V-in, which makes peak current much less.
And, while I have your attention... Is there any plans to publish some more documentation on the board, like actual schematics/layout (that aren't part of some excel file), and perhaps production files for both the evalboard and the add-on led board? Not really going to help my situation but maybe for others who want to make use of it?