Tandems afford some great choices for location of the evolve motor without having to weigh the loss of the Drive function. I doubt that location seriously effects efficiency, but there are some other considerations that may be more important to you.
1. Rudder control -- the large Hobie rudder provides more of a hands free operation than the evolve rudder. There is a tendency for the evolve rudder to wander left or right depending on the amount of power is applied, so it's hard to keep it hands free at low and high power levels. Also, there is more effort in turning the evolve rudder because of the gyroscopic effect of the spinning motor.
On the other hand, the evolve rudder can really spin the boat around in a
very tight circle. This may not have much practical value, but it sure is a lot of fun!
2. The evolve rudder mount requires the current pull-handle version of the Twist N Stow rudder; the the drivewell variant does not. That may or may not be a factor depending on the age of your Oasis.
3. The rudder mount gives you 3 simultaneous power options rather than 2. As a matter of practicality I doubt that this has any significance though.
4. If sailing is an option for you, the Hobie large (sailing) rudder is needed; the evolve rudder is not sufficient to control the boat under sail without power applied.
5. The drivewell position is more versatile. The evolve is easy to remove if you want to use to use the Drive there on occasion (guests, etc.), whereas the rudder position is more permanent. If you are (a) out of power or (b) don't want to use the motor, the rudder mount cannot be retracted to reduce drag without losing steering control, whereas the drivewell mount can removed with no degradation in function.
For fishing, the advantages of the drivewell mount appear to outweigh the rudder mount in most cases. You 'll have better hands free fishing, faster rudder response and much better low speed (power off) rudder authority using the large Hobie rudder.
