You'll find that tank hires are pretty hard to come by in Thailand without diveguide in tow.
That is why you have so many boats hitting the areas like the Similans and the surrounds, because the diving is better there. You can obviously find a better operation which caters to photographers vs the masses. I believe most ops will allow you to wander away from the big group if you have a buddy (or if you know them well enough that they don't bother you
). Thailand is unique in that many of the DM/guides have no idea of what to look for with macro, being fresh out of DM/Instructor courses.
For example off the king cruiser wreck, there are sea moths in the sandy area but it's deeper. But I'll refrain from giving insider info because I spent years finding those places 
"because the diving is better there"
Sorry Drew, I don't quite agree here, the diving near shore in some places is amazing. I done a night dive off Phi Phi, very close to shore. It was so close to shore I could have dived it from the beach! I found bobtial squids, tigertail seahorse, a whole array of cool crustaceans and more...
The problem is, the general standard of dive guide and operators there suck. Many dive guides that I met in Thailand simply get into diving coz they think it's cool to have a big watch and try to have sex with the tourists. Mark Strickland is the man for Thailand, he knew his stuff and had a passion for it too! My guide was a night diver specialist, well this is what he said anyway. He shot like off like a rocket down the reef, when he got to the dive shop he was raving about the stuff he saw, saying he'd never seen most of the critters I showed him. Sorry but this is what you get with your average PADI dive guide.
My liveaboard experience in Thailand was also not so hot! Absolutely fantastic photogenic and historic boat (The Junk) with fantastic crew, outstanding food, however too PADI oriented and too much emphasis on the big animals we might see! Hey, with 7 or more other dive boats all trying to see the same big animals, you've got no chance. I went off from the group many times and had close encounters with mantas and sharks, though the group following the guide had to hold on in a strong current with about 50 other over excited divers! That's not quite my idea of fun!
I was told about Kata beach being great, so I'd say go with Spen, sounds like he knows his stuff and he's a shooter too!
Spen, If I get back to Thailand again I may like to look you up for some shore diving too if that's cool with you? How are the nudibranchs from shore and is it possible to night dive at some of these spots? Please PM me about this too if you don't mind!