Subject: how does a TOF reflector work?

I am trying to understand how a reflector work.  So far i understand that when
ions with the same mass enter the reflector, the ones that are traveling faster
enter sooner and go in deeper than the ones that are traveling slower.  This is
how it compensate for the different velocity distribution.   So what happens to
two different masses (say two different isotopic mass of the same molecule) 
with the same velocity enters the reflector?  Do they penetrate the distance? 
Probably not, right? because that wouldn't improve the resolution...kinda
confused.  

Re: how does a TOF reflector work?