You're welcome!
The Mitsu warranty does appear impressive, yes.
As for the Mirage numbers... have a look at the Scion iQ or the Smart Fortwo for an indication of where we think it will land, perhaps slightly better: The Canadian iQ
is rated at 6.5 L/100km city, 4.7 L/100km highway; Fortwo
is rated at 5.8 L/100km city, 4.7 L/100km highway.
If you're managing to average 6.0 L/100km from your '03 Focus in the summer (which is the highway rating of the 5-speed Focus), that suggests you're an above average eco-driver in sub/urban conditions, or most of your travel is relaxed, moderate speed highway driving (at or below the speed limit). Or some combination of those two.
You should be able to achieve similar results with another vehicle, unless its rating is way off (and we know that does happen).