Well thats how its possible for a horse like Altior to be faster even than hurdlers, because he's of a greater ability hence practice beats theory. Chasers by default have alot more scope over fences but its very hard to compare even the same horse over different obstacles because some jump the hurdles like fences and some very tall horses like Douvan simply hurdle the fences. The RP time difference is because in practice trainers choose the speedier types to remain hurdling and the ones with scope chasing. For a full race where they jump 8-10 fences that amounts to a second/two or more, but we were talking about from 3 out, which means only 2 obstacles and that amounts to fractions of a second which really isn't relevant.