This was my finding as well, between a B22 and the HP4. But it was very, very close. Honestly, I could live with either.
It was a while ago, but when I compared the two, there was a difference in tone, and I preferred the HP4's. I'm not sure that it was a right/wrong thing, more of a preference. Maybe the B22 was more transparent, and the HP4 too lush, but it seemed at the time that there was just a bit of grain or edge, maybe a slightly stronger attack in the B22. It seemed like the HP4 was a little gentler.
I cant remember for certain, but I want to say there was a bit more bass quantity with the HP4.
I have no idea if it was the tubes/transformers/other that made the difference, its just what I heard.