well why don't you tell him what you told me that there really is nothing that you can keep in that tank. So sell it and buy a 55gal or larger and don't waste your time with anything else. Not exactly a helpful attitude you have and to be honest most of the info about sizes is bunk. a 2" neon tetra? I have never even heard of one.
Some bettas can tolorate tankmates and some can't. Pygmy cories are supposed to be compatible, but my betta is particularly aggressive and pretty much decimated the cories before I could separate them. The fish store guy (who said he'd been doing this for 30+ years) told me he's never seen this happen. Yeesh. So, I haven't been able to keep anything in with him. In his defense, though, he came from a very large shallow tank used to display plants for sale. He had a lot of room to rule the roost (I kinda feel guilty for keeping him in his own 10 gallon).
Just a quick update- I decided I really loved the rasboras, so I got 5 of them, and no cories. They are all doing great together. Amadeus is a lot more active and less bored, and the rasboras are schooling together beautifully. No aggression from anyone- Amadeus just flared a bit while I was acclimating them, but it's been 6 days now, and they are getting along perfectly. They really are gorgeous little fishies! :D