Early on when I first started to take my MINI to the track I tried the Hawk HPS brake pads on the front brakes. While they were good on street they were horrible on the track. They faded out and I had almost no brakes. The Hawk HP+ is a much better brake pad for the track, however, it has a low temperature range. Not suggesting to switch from the Carbotech 1521s. Just providing info from my experience.

I don’t know what kind of temperatures are developed in the rear brakes. This might be a consideration and the reason I find matching pads front to rear work for me. The rears might be reaching temperatures beyond that which can be handled by a lesser pad. This may be a reason the HPS pads in the rear provided unsatisfactory results for you.