T20 vs F20 ... F20 is a front loaded horn design with more chunky proportions, more volume and more efficient in material use, but its form factor makes it harder to hide. When made into that kind of size, it tends to be bandwidth limited like a tapped horn. Tapped horns are always bandwidth limited, but with a FLH you have a chance to get them to run over a wide bandwidth. Not that you need it here.
Now for a given size and extension, a tapped horn will tend to protect the driver from excursion to a lower point, but with no sealed cavity, you ideally need a rumble filter. T20 controls excursion to 20 Hz nicely. With F20, at 25 Hz the excursion jumps right up, but then reaches a point where the sealed rear air volume stops it going further. Still, excursion limits come in much sooner. So in terms of getting max SPL, the tapped horn wins. Both seem to occupy similar territory in terms of their sound. They are brutal, funky, tactile, forceful.
When I had them both in the same room, I didn't really compare them doing the same job. One was in the corner, the other plonked in the middle of the front wall. They are gigantic in any room, you can't really shift them easily. Although, I'm proud to say I managed to get my T20 from the workshop into the HT room on my own when I finished it at 11pm one night. Not bad when you consider it can't make it through the workshop door way without going on a very difficult angle, it's 2.35m tall!
The horns definitely have a different sound. If I could put it this way. Horns for rock, pop, bass heavy music and home theatre. Sealed for acoustic double bass and where you want accurate bass. But everyone should experience a bass horn with some time to spend with them, at least once. I will soon be using both, kind of a cake and eat it too setup.