I just had a very 'interesting' conversation with AA regarding COS bonuses. I recently had a paid-first class flight STL-ORD. The flight posted as 675 miles - the same as the Y class flight I had ORD-STL. I asked why. Here is AA's answer:

For the F flight:
258 - Flight miles
129 - COS bonus
113 - top up to 500 miles
125 - AA Gold bonus

For the Y flight:
258 - Flight miles
242 - top up to 500 miles
125 - AA Gold bonus

So, in effect, there is NO class of service bonus for flights less than 500 miles.

How do the other airlines compare?

Cheers,

'toad