OP, I think I found your test on TR. I'll let you post the link if you want. So, assuming I got it right....

If it's the one I think it is, the power targets for the workout were based on the default FTP of 200W. The rider took at least 30 seconds to ramp up to power on both intervals. He was able to hold the target 230W until about the 2 minute mark of the first interval. His heart rate was climbing throughout each interval. And he had gas in the tank at the end of each to spike his power to (on average) the 300W range.

When I do the test (and I'm not very good at it -- I usually do the first interval a little too hard and fall apart a bit on the second), my power ramps to target in seconds as I accelerate, my heart rate gets to the point of plateau within 2 minutes, and I have nothing left at the end for any kind of finishing sprint.