for what its worth, the shot from overhead with that amount of fender being wider than tires is very similar to the distance I've had on a couple of bikes of mine for a couple of decades, and the fenders have done their job well (water spray wise)
In your other shot however, the angle of the shot doesn't really show the actual clearance between the tire and fender. I will take some photos from lower down of the fenders on my two bikes to give you an idea of what clearance I have, and have pretty much not had any issues of stuff jamming inbetween tire and fender.
As you say, wider will give you more wiggle room, but you may have to do what you said, to contour out some room at the top of the fork.
In setting up fenders on my Troll, I went very conservative for fender/tire room, we're talking more than an inch clearance with mud in mind, but the other bikes used for eons are much closer and have worked fine---just remembered you want to go off road more, which certainly will increase the risk of picking up a stick or whatever, so in the end, perhaps more room is the best route to go, but thats up to you.