David,
I think TAD recommends about 2 feet as a minimum. That's where I have mine. Yes, they are front ported and I think 18 inches will be fine. I'd have to try it at 18 inches and hear how it sounds.
Metralla,
I use a Dartzeel 108, CJ ART monoblocks, the Job 225, and a Carver Black Magic for fun. The Carver is a little underpowered but if you lower your standards a little, it can sound really good. I think the Lammms you have might be fine. The TADs are 86 dB at 4 ohms but a fairly easy load. The Job has me surprised. I am enjoying it more than any other solid state amp so far.