I don't think the ratio is as important as the absolute range. For road trips, I like having at least 300 miles of gas-only range. That means I can make a typical road trip without having to stop for fuel along the way, or just once on a longer driving day (and assuming an empty battery). I personally could get by with say 100 miles, but then it gets annoying to have to watch the fuel level all the time and make frequent stops. It would add time to the trip, and then I would get complaints from my wife. She would want to take her ICE vehicle instead, which happens to to get over 450 miles before the light comes on -- very nice on long trips or when more fuel is needed for towing.
And there are some areas in the western states where you really would need extra range to make the next gas station. Remember, these vehicles have to appeal to people used to ICE vehicles and their typical ~400 mile range.
And the difference between a 100 mile and 300 mile gas range is just designing in space for about 5 gallons of additional fuel. Not hard to find that space in a regular sized car.