Share 'Scupper Hole transducer mount Tarpon 140'

I am setting up a Tarpon 140 with a Lowrance Elite 4 DSI, and want to use a scupper hole mount. My two questions are: Is one scupper hole better than another? and, Would the transducer perform better (bubbles & turbulence) mounted in the 'trough' of the hull, where it is protected; or extended below the plane of the hull? The latter increases the risk of rub off. Thanks for your help.