Why Does My Power Required Curve Lack a Reverse Command Region?

[subsonic]

Can someone help me. Why does my power required curve doesn't have the region of reverse command? It goes up from vmin to 230mph. It never goes down. Thats not normal for the power required curve.

Attached is the region of reverse command that a power required curve should possess.

Details:
Propeller fixed pitch
engine 107hp @ 3300rpm
clmax= 1.35



what should i do? Is there a possibility to have a power required curve
without region of reverse command.

 

[CWatters]

If it's got a fixed pitch prop how does it manage to provide reverse thrust?