if the 1.5T HRV is using same suspension and absorbers as the RS Hybrid EHEV, then high speed i am 100% sure will > cross

cuz the car is retardedly stiff (and harsh)
first gen HRV is overly soft, so from complaints and feedback, Honda Malaysia Lazy engineering > max stiff on the other end of the spectrum. but that will mean highway stability (and to an extent, cornering, assuming smooth roads) will be very good, no floaty feel at all.

You can't estimate with just RPM without consider load.

The only absolutely true measure is the air flow throw the throttle body (hence TCR, GT3 racing using air restrictor in their BoP Balance of Performance, which is basically a standard size cone for every team).

Modern engine varies a lot around the ideal 14.7 ratio, even more so for the small displacement turbo with ultra lean (stratified) combustion mode at low load on both low/high rpm.
On the flip side, on high load extra fuels are injected just to cool the engine for both NA/Turbo, just more severe in turbo case.

My car easily varies between 20km+/l to no more than 5km/l.

Rule of thumb, don't think of the rpm, think of your own throttle input (although drive by wire means it is also damped by ECU).