I do not think you need to concern yourself with how close you are to the fish. You should be more concerned with noise spooking your fish. Just line the inside of your boat with something that will keep the noise down. Afterall, many, many years ago people fished with a straight length of pole with about 2 foot of line attached to the end with their lure attached to it and dabbled it into the shore weeds and they caught the fool out of fish. Sound proof the inside of your boat and go fishing.
Fly fishing and fly tying are two things that I do, and when I am doing them, they are the only 2 things I think about. They clear my mind.