I've done Kevin's course, and respect his experience and knowledge, as well as others who say you can do a good job with sufficient dwell, agitation and a wet vac.
However, on job after job we do all the dwell & agitation, then end up winding the pressure (and heat) on the TM up until it's doing the job.
Last one was a riven pattern ceramic glazed tile, 6" sq, that some tit-head had put a topical sealer on. We used hi pH detergent with honing powder, then solvent stripper, rinsing between, but to do an effective job we ended up winding the pressure up to 2,000 psi (through an sx 12), then detailing with a Woodbridge HP hand tool at the same pressure.
I simply don't believe you could have done the jobs we've done without recourse to 1,500 psi or above. Convince me I'm wrong.