If a rear-ported speaker is tuned appropriately, there's no reason why it can't be used close to the wall or even in a corner. Audio Note speakers are designed to take advantage of boundary reinforcement from a corner, and they're rear ported.
You might try lowering the tuning frequency. You can do this by either lengthening the port or decreasing its diameter, or both. I've never tried this, but here's what I suggest:
Buy a piece of PVC pipe from Home Depot whose outer diameter is slightly smaller than your port's inner diameter, so it will slide inside. Cut it to roughly the length of your port (a little longer is okay, as you will probably be trimming it later). Wrap electrician's tape around the outside of the PVC pipe at one end (the outer end), enough to get a snug fit inside your port. This will lower the tuning frequency, hopefulling transforming what once was boomy bass into deeper and tighter bass. If the bass is diminshed too much, that means the PCV pipe is probably too long (tuning frequency too low) so shorten it some and try again.
A cardboard mailing tube will also work. Or a bunch of plastic drinking straws cut to length, tightly packed into the port until they deform into a hexagonal pattern and friction-fit in place. You'd probably have to remove a woofer to do the drinking straws though, as until there's enough of them to friction-hold in place they have a tendency to fall inside the box.
The tradeoff is, at high volume levels you'll get more compression in the bass region (less impact) due to the reduced port diameter. And at high volumes you'll probably get turbulence that can cause port noises (though it's possible that the tightly packed drinking straws may actually reduce turbulence; I'm just not sure). Will these tradeoffs be audibly significant? Only one way to find out.
Duke
You might try lowering the tuning frequency. You can do this by either lengthening the port or decreasing its diameter, or both. I've never tried this, but here's what I suggest:
Buy a piece of PVC pipe from Home Depot whose outer diameter is slightly smaller than your port's inner diameter, so it will slide inside. Cut it to roughly the length of your port (a little longer is okay, as you will probably be trimming it later). Wrap electrician's tape around the outside of the PVC pipe at one end (the outer end), enough to get a snug fit inside your port. This will lower the tuning frequency, hopefulling transforming what once was boomy bass into deeper and tighter bass. If the bass is diminshed too much, that means the PCV pipe is probably too long (tuning frequency too low) so shorten it some and try again.
A cardboard mailing tube will also work. Or a bunch of plastic drinking straws cut to length, tightly packed into the port until they deform into a hexagonal pattern and friction-fit in place. You'd probably have to remove a woofer to do the drinking straws though, as until there's enough of them to friction-hold in place they have a tendency to fall inside the box.
The tradeoff is, at high volume levels you'll get more compression in the bass region (less impact) due to the reduced port diameter. And at high volumes you'll probably get turbulence that can cause port noises (though it's possible that the tightly packed drinking straws may actually reduce turbulence; I'm just not sure). Will these tradeoffs be audibly significant? Only one way to find out.
Duke