Field - Field futures exacta payout?

[Marlin]

Wondering how it is handled in the futures betting for the exactas.  As very well possible the Derby exacta can be field/field.  However, that is not one of the betting options allowed in the futures pools.    
     As I look @ the future pools exacta payouts, there is NOT field/field payout.  But they took plenty of wagers on everything else.
     Seems illegal to take bets without the possibility of an actual winning combination available (field/field) to receive payment of that exact order of finish?
     
    Thoughts, or am I completely not understanding?

[BB]

In the event of field horses getting into the first two (or more) top spots, they will pay out to the highest-finishing non-field horse.