Attached is an example of the Old Town short deck with a decal, so you can see how it is placed-- centered in the wider part of the deck.
The canoe in the picture dates from the '60s and the deck itself, as well as the decal, are different from yours, but looks like a good example of "decal placement" to me.
I snarfed the picture from one of Robert Ross' ads-- he gets credit for the picture.