Regarding fuel average..
dear all i must say that 20 is the realistic average of aqua...but i worked on my driving again yesterday and extracted a healthy average in 40 degrees within city...
just took care of few things and wohoo,25+km/l..
-very light foot while accelerating from zero.
-try to take your car to 40-50km on battery.
-keep your speed under 60.(should not be a problem within city)
-after reaching 50 km/h, leave the accelerator to let battery charge on deceleration.
-keep your climate control on 26-28 degrees.
-when going down the bridge leave the accelerator alone.
-dont let the acceleration go out of economy bar on petrol,this saves a lot specially when battery is being charged and car is feeling heavy.
-switch off ac on elevations like bridges.
-put car in parking gear on signals,this lets the battery to charge.
in short its all about your foot,if i can control it,anyone can.(because i used to have vitz previously and used to stand on its accelerator). One good battery fill up and you can gain 2-3 better per km average by driving intelligently.
in case you feel this all is a futile job and frustrating, hit the gas..you will get 19km/l average and honestly that is still way better than non hybrid cars in this intense heat and air conditioning on... 
