No, alloys are not responsible for fuel average, fat tyres have something to do with the mileage, that too not much, rim size should be correct.
Have you checked the condition of the spark plugs, they are 8 in total.
Also, change your car's CVT fluid with Honda's original one, it will cost you some money but its worth it.
BTW, Vario's average is very good better than my 1000cc Joy, i think it is 12 to 13 kms/liter, now i dont have it so cant recall the exact figures
How much has your car done? you may also need a throttle body cleaning via carburator cleaning spray, no big deal, first get your car's throttle body sprayed and then change its spark plugs if they are too old.