I own a pair of Coatbridge built Legacy Ardens, and the footprint of my room is close to yours at 17’x13’. The speakers do not overwhelm the room with excessive bass given their front ports, and are quite flexible regarding placement. However, toe-in makes a significant difference in sound. Cross-eyed toe in works best in my room.
I think the main difference between any Tannoy and your JBLs is the point source design vs. the compression horn of the JBL. The Tannoy may sound more cohesive at the expense of sound dispersion. There is a sweet spot when sitting in front of the Tannoy and it’s not the widest if you’re chasing the ultimate in sound staging.
If you’re looking at the Arden (Upscale’s “blem” pricing is attractive), you’ll want to consider raising them up depending on your seat height. Mine are lifted 8” off the floor to raise the tweeter.