Indeed it would be nice to have even more ground clearance in Crosstar. In theory it should be possible to change to longer springs, or stiffer springs, or put some spring spacers to lengthen the existing springs, but I have no experience about this in practice.
The ground clearance of Crosstar is only about 1 cm higher than the other Jazzes, I measured it once at my local dealer. I think this 1 cm comes from the Crosstar's tyres that are 17 mm larger in diameter than the tyres of the other models. So it could be that Crosstar probably has the same suspension as the other Jazzes. In the specs it says that Crosstar is 3 cm taller than the other Jazz models, so the missing 2 cm must then come from somewhere else, maybe from the roof rails.