if you wanted a knife that would get as large as a clown, you could get a black ghost knife. they top off around the 18" mark with some growing a little bit larger
If you are deadset on an aro, then id suggest a silver over a jardini. The silvers are more flexible, but IMO a 6x2 (I'm assuming) footprint is not big enough for any aro. What about a lone puffer? Fahaka's are amazing! Like little puppy dogs. A 220 would be a perfect tank for 1.