Bigger is always better for teepads. I don't recall ever not using an entire teepad, no matter how big it was. I want it wide and I want it long. Level is nice, but level only lasts so long. When it gets muddy, the dirt around the teepad gets carried out onto the fairway by the players and the pad gradually "rises." Mulch helps, but only so much.
I want a teepad I can start my run up on. I almost always start off the back of the teepad and my first step is onto the pad. That's dumb.
My ideal teepads would be cone shaped. 4'-5' wide at the front, 12' wide at the back, 15-20 feet long. Yea, it's a lot of concrete, but you only make these things once. If the stupid thing is 3x6 feet, I don't even want it there. It's just in the way. Use a dirt pad instead if you can't afford a few more bags of concrete.