Here are my thoughts on the subject;
1. Yes. Std53 defines closing ratio in this manner. (I don't have the latest version at hand to show the reference)
2. No. By definition its a dimensionless number being the ratios of areas. I think it's a question of static well and operating pressures rather than the dynamic case during closing. (I doubt whether a ram seal could sustain integrity for long with any fluid flowing past at a pressure of 15ksi while closing)
Every ram has a closing ratio, most lower rated rams can close against
their RWP at operating pressures lower than 1200psi. Only when the RWP
is higher, like 15M and above, is a higher pressure required because of the operating cylinder geometry constraints.
A larger operating piston (lowering the closing ratio) would require
more volume, more volume means more bottles and bigger hydraulic lines
to ensure closure within the maximum allowable time.
On a standard koomey, the manifold pressure is regulated to 1500psi. If
it operated this particular ram, it could only be closed (theoretically)
on a 10.5ksi (1500x7) well pressure. So closing ratio counts.
would be an interesting test to see what pressure initiate ram movement
as a measure of the system friction. Perhaps the manufacturers have
done this test for science?