I won't be of much help as I own a 498rc2 and use it with tripod. I did intend to use it with a monopod as well, but never got the opportunity. I do agree with CGW that ballheads are not the best solution for use with monopods.
Digression that has nothing to do with the question:
Who would tell that a sturdy thing like Manfrotto 498rc2 could be rendered useless in 5 seconds by a bare-handed 2 year old. The main knob unscrews easily and nothing prevents it being pulled out. The problem: The thread of the knob is hollow and contains a domed insert which, my guess is, does the tension work. What holds the insert in place? Nothing except some grease (I went to a Nikon store and checked the head). So my 2 year old son unscrewed the knob, took it out and threw it away. I found the knob because this happened in an apartment and the knob is big enough. The insert is tiny and MIA (and no, he didn't swallow it).
So, if you own one of these, be careful not to unscrew the main knob all the way or you can kiss about $30 goodbye and can't use the head until you find the part.