I concur with mental4astro. Note also the 5x powermate magnifies up to 7.7x as the increase from the top surface increases. See
http://www.televue.com/engine/TV3b_p...p#.U4gMOHKSy5I
If you have the 0.5x reducer and 5x Powermate try it and let us know, but I wouldn't buy a reducer expecting it to work. The 2.5x Powermate certainly will work. However note from the same chart above that the 2.5x Powermate magnifies less at an increasing distance from the top surface almost matching the 2x Powermate.