I removed our Mud Flap in late 2012. I did not measure how high it was off of the ground. I removed it because we had gravel chips inner paint of our CRV, and many times several stones at the base of our windshield. We were planning a trip to Alaska, and after reading Pro/Con on Mudflap vs Non Mudflap - and knowing what I'd seen in 2+ years of with Mudflap - I removed it.
We had less gravel at the base of our windshield.
About 8 years later, our same toad does have many 'Road Warrior' signs of travel. Would it have been less with the Mudflap on? No way I can say for sure. But, IMO, yes.
Now, lots of dynamics involved. What is the length of the coach? Tag or Non Tag? What is the length from the furthest rear wheel (Tag or Non Tag) to the back of the coach. Does the last furthest rear wheel have a Tire Guard, or not? (Ours did, and suspect that handled 80%+ of the rocks floating up form this wheel.
We did have a Tag, so our Drive tires were that much further forward...
Apples to Oranges in what may work for some coaches, vs others...
I never felt the need to put our mudflap back on...
04 40' Allure with Tag.
We frankly had more damage from rocks/gravels from vehicles either coming toward us on tight roads. Or passing us. Then I feel was ever generated from our own Drive/Tag. Again, on our specific coach and it's layout of Drive/Tag to where the Toad was waiting for impact
I did know one gent with a Alpine. The hung his Mud Flap up as high as he could get it. He drover 5K with it down, and 5K with it up - and on his coach with tag, he felt the had less damage to his Toad with it up, then down...
(And yes. It's for sure not scientific! His and my opinion...)
And, I do know many Owner's who swear that the Mudflap's are a positive protection for the toad form gravel tossing up...
So IMO, the best thing to do, is try a few thousand miles each way. And make your own conclusions for your 'specific' coaches
Best to all,