The mileage figure actually DOES attempt to equate to the total cost of travel, but after X number of miles, there are economies of scale. In other words, there's going to be more wear and tear on your car if you go 25 miles on 4 nights rather than going 100 miles on 1 night.
The thing is, I have an SUV but still can't fit all 5 guys (not to mention 6th man) in my vehicle. Unless someone has a van or we rent it, 6 going together isn't happening. And we have had games were 3 or 4 of us travel a long way and 1 or 2 are local. The 60% would probably work well in those cases.