A trick you can do that will bring fender clearance to the same clearance as the current tire-seatpost clearance is to cut a narrow ellipse out of the fender. To do this, put the fender on (no wheel needed) and notice where it hits the seatpost. Notice how big the gap is between fender and seatpost 3" above that contact and 3" below. (Should be nearly the same.) Find a good feeler. (2 quarters, perhaps?) Now use the feeler to mark the fender beside the contact point on both sides.

Remove the fender. Draw a narrow ellipse from the lower contact point to the upper at the width of the two marks at the contact point. Dremel the fender to the ellipse. (I'd dremel to a narrower, shorter ellipse, trial fit and expand to what works best, putting in the wheel periodically to get the clearance off the tire consistent with what I want at the brake and behind.)

End result - a nice, snug fitting fender that looks perfect. And fits so snug there is no wobble at all until well behind the brake.

Edit: You may need to dremel out for the front derailleur as you do this. And you may find you have little material left at the FD. You can epoxy a fiberglass to the fender inside from a couple of inches above the FD to the same below. Perhaps 1/2" strips pf fiberglass. Since these will be right out at the edges of the fender, a clean job wouldn't affect the tire clearance and being inside the fender, no one sees it. (Use two part epoxy resin. WEST System or the like from West Marine. I bet Tap Plastics has an equivalent. (You want lots of working time. An hour or more. The stuff you mix up and need to tidy the end of the job will set up faster in the mixing container than the resin you are working with. Does mean you will not be trimming the tape edges until quite a few hours later. Probably not ready to use the next day.) Smallest bristle brush or largish artist's brush. Remove as much excess resin as you can. Fiberglass will "float up" on thick epoxy and leave a wavy surface you didn't plan on when you finished the job. And DON'T go back and try to correct that!! At the semi-set up stage, the resin is impossibly sticky and completely impossible to work with. Epoxy and lacquer thinner for cleanup. Masking tape or painter's tape to protect everything you do not want to epoxy. A very sharp trim knife to cut to the tape edge when the epoxy is 90% set.)

A project, yes. Bu the result is sweet! (I don't know how well this would work with the "slippery" Planet Bike fenders. Works really well for the SKS ones.