I've been looking all over the web and can't seem to dig much up on the subject of using COBs on a smaller scale. If you know of any info please share a link!
Got a 12x24x30" cab and thinking of different setups. 6 Vero 13 maybe?
You can also look at CXA/B 1816 and 2530s. Also consider Vero 18s at lower currents. The Vero 18 runs at slightly lower voltage than the 13 which can be useful depending on the driver you want to use.
I'm running a smaller cab right now 11"x20"x29" and have two cxa-3070 mounted through the ceiling. I run dimmers to control the intensity when they get to close. Works great