I have 2 Farrell combs, a black one for a G chromatic and a white one for a C chromatic. On both of them the top octaves play quite nicely. The only problem is that there is some obvious air leakage in the top octave of each instrument that negatively affects their response but I believe that is due entirely to leakage from the traditional 4-piece slide assembly.
Joel Anderson, the master Swedish harmonica customizer, is now milling his own chromatic combs and doesn't have ramps in them. I haven't discussed the reason why with him, but I would have expected that someone like him who works on every single aspect of a harmonica to squeeze every extra bit of performance out of it possible would have included ramps as a feature of his CNC milled chromatic combs if he thought it would have improved their performance.
Probably the best chromatic I've ever had is an SCX-16 with a standard unmodified factory-made ABS comb which, after dipping the slide assembly in a very shallow tray of water, is very loud and extremely responsive from hole 1 to hole 16 with no ramping required!