My (future ex-) Widemove scanners have standard mirrors (5x10mm) and can scan at 90° with my 3.5mm laser beams. The trick is that you can move each scanner individually (verticaly and horizontaly) so first you can adjust the X mirror height perfectly to the incoming beam to have no loss, and secondly place the Y mirror very close to the X mirror so they don't need a mega-long Y-axis mirror...