I wasn't aware that they "self adjust". Usually, you can buy them in different "degree" specs that will work for a narrow range of deadrise (or there's a hull adapter)... meaning, you need to know the deadrise at the spot you're mounting it.
But, aside from that... just git 'r dun, already! Drill the hole in an accessible location, taking into account what's been mentioned above and the owner's manual for the ducer. Where someone else mounted it doesn't mean you have to mount it there. Put it where it works best for YOU. Or, if you're not up to the task, just hire someone - it's about an hour to two hour job, tops, to just install the ducer.