The height increase depends on set-up and prop diameter. The Bravo I XS is a large diameter propeller. Typically, those running it raise the engine 1/2″ higher than the standard transom height. I’ve seen some run their Bravo I XS engines as high as 1″ above the standard height. It all depends on the application and what you want to get out of it. Hole shot – mid-range punch or top-end speed. A hydraulic transom plate enables the operator to experience the full capabilities of the Bravo I XS. Bottom line, you have to try and figure out what works best for your application.
It's worth pointing out though that there is nothing special about the proportion here - why have you chosen it as the cut-off point for your alternative hypothesis? For example, why not have as a null hypothesis that a third of people choose each option? or any other set of probabilities, perhaps based on an experiment of having people fill in the survey having received a placebo. Having said that, there is strong intuitive appeal in the cut-off point and there is no doubt your experiment shows statistically significant evidence that more than 50% do report an increase. The only question is, how does this compare to the percentage who report an increase under other circumstances? (which is not what you've asked here, so I won't worry about it).