Sport mode gives full power all the time even below 26 miles battery range as far as I can tell. I would imagine that you could even drop battery power below 15% which is zero battery range if you drove like 'a bat outta hell' for a long enough stretch. Seeing as it only takes 35kW to cruise level terrain at 70 mph, it is just that the engine gets to rest more often at battery levels above 26 mile range because it is no being forced to sustain anything more than that.