I haven't tried it right now, but I am pretty sure that in your case the voltage from the HP-cutoff dial is summed with the voltage from the modwheel. That said, moving the modwheel acts like turning the HP-cutoff dial to the right. So it's like going from 5-10 and not from 0-5.
I have the System-1 for a few months and received my MS 20 Mini yesterday. Played with iMS-20 on my iPad for quite a while. I personally would never trade one for the other, because I am finding both to be very different. The System-1 is a Roland, so it sounds well behaved, more exact/polished ...