Whoa!! So much to unpack.
Let's start by having you read this web page:
http://barrystiretech.com/loadtables.html
This will ask you if you read the page on Tire Standardizing Organizations. Do that, too.
3 things you should pick up:
1) That the rating pressure for Standard Load P metric tires is 35 psi - and even though the max pressures may be at 44 or 51 psi, this value still holds.
2) That there is a note that it is PERMISSIBLE to use 44 psi and 51 psi - hence some tire manufacturers will list one of those as the max pressure. So don't read too much into that, because it doesn't say when to use either, so the decision is relatively arbitrary.
3) That the load curve is NOT proportion to the inflation pressure, so the formula you are using is wrong.
And a couple of tidbits:
What is the USTA? Did you mean the USTMA - US Tire Manufacturers Association? If so, then be aware they don't publish load and inflation information - but the tire standardizing organizations do, hence why I want you to read my page on the subject.
The 1996 Ford Contour? Only the SE version had that pressure split. All the other versions used the same pressure front to rear. (Source: The Old Timers Tire Guide)
Why would Ford do that? It has been known for vehicle manufacturers to tweak the tire pressure to get certain handling characteristics. My opinion is that they shouldn't do this, but they don't listen to me.
There are more things I want to talk about, but I don't want to overload you with information, so I'm doing this in steps.