I can’t, but not because I don’t want to be.
Couple of things, and then maybe someone else can chime in:
Steve’s appearances on podcasts (like a lot of other coaches, etc) was intended to drum up some business, and at least back then (pre-lockdown), it seemed to attract a few new clients. The heart-rate cap was really just a compromise for folks who couldn’t or didn’t want to run through a suite of testing that he used to assess each rider (lactate, perhaps NIRS, biometric assessments). A foot in the door into his process. I’m not sure any single thing that Steve did was revolutionary, but in its totality it was highly effective (for me and a few dozen others on the coaching site, as well as private consults and clients). Most of us were in our first five years of cycling, and didn’t fully understand or appreciate the types of training plans we were trying, the jargon we learned, or really what to do. We constantly second-guessed ourselves. IOW, we were TR users.
From bits and pieces on his coaching site from a few years ago, I can say he likes Billat intervals, but to reduce it down to that would be a big over-simplification. He values race specificity when it comes to intensity. He then works with you to see what you can recover from the fastest. Intensity doesn’t do you any good unless you recovery from it. He’s not going to go down rabbit holes of physiology discussions, other than just to discuss what he has learned with his coaching. He will look back over his database of former riders, assess you, and go “ok, this worked for a rider I had before who was like you, let’s try it”.
Here’s the answer: unlike tempo and endurance (for which Steve felt everyone should do at all stages), high intensity was very individualized, so much so that he likely wouldn’t answer this question. What he prescribes one rider would likely be very different to another. Therefore: I don’t know what he uses. He uses it all. 
You will find a lot of his riders are fairly coy about what he had them do. Part of that is the individual nature of the work, and part of that is that Steve is trying to protect his “intellectual property”.
One of the very first things he would do (without being confrontational) is question the veracity of what you wrote above. Can you really do that? Did you do it w/o a drift in HR, drift in lactate (or maybe now something with Moxy)? If you did the above tempo and everything was flat as a pancake, great. If you held the power but things weren’t flat then you didn’t really do it. This is a fundamental difference in philosophy than you either embrace or not. He is a “balance point” guy. It’s not that he thinks anything magical or different is happening at these lower intensities, it’s largely a fatigue management strategy because it’s a time in zone game. Who cares about 15 mins at 90% FTP when I can do 120min of mid-tempo (that’s obviously contrived and not really realistic, I’m just trying to make a point). They are the same adaptations, so more minutes is…more better :-). So many folks think they can do that by feel but there are dozens of thread on here that strongly indicate that most less experienced riders simply cannot.
I don’t remember seeing anyone come on his site who could lay down 60’ of what they defined as threshold (much less how he defined it) without drift.
But if you can, cool. Time to start slamming some intervals or using races to get your intensity, which by and large is what happened anyway, because ppl would do tempo and endurance until the season started. Early races (bookended with endurance riding) ended up being the intensity, for better or for worse.
The main thing I learned from participating on his coaching site was that I could get very fit on 10-12hrs without doing hardly any intensity. Maybe times have changed. I don’t know. And most of the hard stuff I did was cross racing or unstructured hard group rides.
