i have a cultus 2007 vxr n it is giving 170+ in city without ac with one cylinder,, ur car gotta efi engine it should give better result,, if mileage is not improved after tunning,, u should change ur cng station,, n also told ur driver to drive car slowly n avoid fast acceleration,, ask him to change gear at 2-2.5 rpm maximum,, becz fuel avrg highly depends uponn way of driving,,
if it does not help then go for cng cylinder cleaning if possible,,, but first thing is to ask ur driver above task