I got the Goldtone clip on mic that Bob Watson referred to. Works nicely and fits all 3 of my resos. Never could get the right distance to a stand mic.. Tailpiece clip on eliminates that problem.
An AKG C1000s mic aimed between the cover plate and the sound holes and 8"/10" off the top always sounded great when my dad played his squareneck through a amp or PA.
That;s exactly how I get the best sound with the same set-up. I can;t use the clip-on because then I can not control volume. Just move away from mike or get closer works great.