Hey,
I'm using the Epson TM60 and TM88 as thermal receipt printers from Access2000.
I didn't had to specify anything on the size of the paper; I selected the receipt as paper source, and could chose between 4 formats. I took the A4 - 29x21cm just like it is a normal A4 paper, and it works fine without any further thing to configure.
Could you maybe specify the brand/type of printer you're using ?
PdtIt