Quantifying rationality
Administer a time-bound maths test to subject A, taking care to explain what the notation means ,etc.
If subject A fails to get a 100%, you can safely conclude subject A is not Homo Economicus. Subject A is acting irrationally.
You can now quantify the degree of rationality. Subject A getting 60% in a test covering the math of optimal asset allocation directly maps to Subject A being 60% rational when it comes to asset allocation decisions.
