I'm not sure why they wouldn't physically fit.
Have a look under the rubber/plastic seam covers on the roof to see whether you have some bolt holes. If you have the bolt holes, then the bars will fit.
On my Stilo, the seam cover had small hatches in it that could life up to expose the holes. The bars fitted with the seam cover in place but the hatches "open"..
X's seem to have a seam cover strip that has no hatch in it.. so you would appear to have to remove the seam cover to fit the bars.
The Cross Plus may have bars *and* some additional trim pieces to fill the seam slot. or it may just have the bars. If they just have bars and the bars cover the entire seam, then you just need to remove your seam cover and fit the bars instead... otherwise you'd need to get hold of any other trim pieces to fill the gaps around the bars... which could explain the "fit/doesn't fit" discrepancy.
Ralf S.