As I mentioned earlier,depending on the differance in height,reach may play a big factor.Weight has nothing to do with it.If there is a big gap in weight,then they will be in a different weight class. I fight at 190-195 for MMA,where most of my opponents have been at the limit of 205 lbs(lightheavyweight division). I have spared with heavyweights.Those at 240lbs gave me problems.They are just too big. Those under that were a bit easier to spar with.
BTW,just for info,I have boxed before,so I know what I'm talking about.