Yeah, once you are above 50 mph and air resistance is the main factor in efficiency then the hybrid benefit diminishes quickly - and it's only the gen IV Prius and newer vehicles that can operate in EV only up to 70 mph, before then it is limited to around 55 mph or lower (the specific speed is model dependent).
but, there is an 8 mile journey (mainly 30/40 mph but a couple of miles at 60) I do on a semi-regular basis. I could get around 70 mpg one-way in our old series IV Prius and the best back was 105 mpg! The same in the UX is probably 50 mpg there and 65 back. The extra 0.2 litres, saloon vs SUV and 16" wheels vs 18" with rubbish RFs makes a big difference.