Many years ago the cap was around 100%. If you have the desire, there are old threads discussing people matching at 90%+ (although IIRC, most repaid within a couple of days). Edit, link added below. I even recall Kev stating that one of their competitors had a marker placed at 100% just so that if it matched, they could call RS and ask if everything was OK.
My guess is that it is an historical reinvestment setting from those times and as such is getting placed at rates that can no longer be set.