I don't run 24psi because the load rating would not be nearly enough, and just like overinflating, the tire doesn't perform optimally.
A Tire Rep. at Tire Rack explained that FORD's recommended tire pressure of 35 psi is a minimum pressure and Michelin's Max Pressure of 51 psi is the Maximum, so anywhere between those pressures is fine. Owners Handbook says don't exceed Tire Manufactures Max pressure which implies you can use more than FORD's recommended minimum.
Why is the Cmax 38 while the Fusion is 35? Could be many reasons, but my best bet would be because Ford was able to round up the EPA fuel economy number by bumping up the extra 3 psi. For example if the Cmax was testing at 39.45mpg at 35psi, by bumping up to 38psi they can get to say 39.55 so the advertiseable is 40 instead of 39. But say the Fusion is coming in at 39.35. Bumping up to 38psi takes it to 39.45 so the net effect on the advertiseable is zero, so Ford leaves the Fusion at 35psi because they know that is the better all around tire pressure.
This doesn't make sense, you only gain .5 mpg going from 35 psi to 50 psi and FFH and CMAX Hybrids were rated at the same 47/47/47mpg anyways , tire pressures haven't changed since 2012. Also FORD used the mpg numbers from FFH for the CMAX and there was a Big EPA Deal made out of that. So FORD didn't have actual MPG numbers for CMAX, nothing to compare too.
The error in your load calculation is the 60% weight distribution at full load. When you pile passengers and cargo into a Cmax, most of it goes on the rear wheels, not the front. I was talking about FFH not CMAX. So at 4500lbs you're probably closer to 52% front (Front GAWR on my FFH is 2440, rear is 2250). 52% of 4500 is 2340lbs, so well within 2734lbs limit. You can find the GAWR ratings on the sticker on the door jamb. You should never be able to get over the Front GAWR unless you attach a snowplow to the front!
So if you add FFH front GAWR and rear GAWR you get 4690 GVWR, then when you step on the brakes hard 70% of the GVWR transfers to the front axle which would be 3283 Lbs, then subtract max load for the front tires at 35 psi of 2734 lbs which means you are 549 Lbs over the Max Load for the front tires or by 20%, which gets worse if you are also turning at the same time, outside tire could be 25% over Max weight, not good. At 50 psi you gain 132 Lbs/ 25% to the over maximum useful load for the tires, which is at least a good improvement to the over Max Load for the front tires.
If I had access to a Tire & Rim Association Handbook I could look up the load ratings for a 93V tire. The ratings are not specific to any tire, they are a standard that all tires must meet. But last time I checked, the max loading was not allowed to increase above 36psi. In other words, the rating for this tire at 35psi is 1367lbs, but at 36psi it is 1433lbs, at 37psi 1433lbs, at 40psi 1433lbs and at 50psi 1433lbs. Not sure if those numbers are still correct, but I know it's not a linear relationship between 35psi and 50psi.
Talking to Michelin Rep it sounded like they were computing it, like they had a formula to determine it. With 30% less psi. than 51 psi, at 35 psi I would have thought there would have been alot less useful load for the tires.