You are tryin to apply logic to the ways of PTC, aren't you? 
Yes, internally the values remember your math... where an entry of 5/64 really is .078125 although at 3 places it shows as .078.
I don't know if this is different in your version. This basically says that new dimesnions will take on these values once they are set in config.pro or in your template files.
config.pro:
I haven't tested this yet, but it seems logical <cough>.