It may be the case that an Epson T20's column setting are off. As seen below on the receipt on the left has the column settings set to "Off" and the receipt on right has the column settings set to "42 column mode".
To adjust this you need need to first turn off your epson T20. Then Press down the feed button and while still holding down the feed button turn back on the printer. A receipt will print up as below.
Hold down the feed button for one to two second to get to the mode selection receipt to print. When it prints you can release the feed button. Shown below is the Mode selection receipt.
Press the feed button three times less then a second apart. Then wait one to two seconds and hold down the feed button again until Custom Value Setting receipt prints. When it prints you can release the feed button. Shown below is the Custom Value Setting receipt receipt.
To get to the Column Emulation you'll need to press the feed button twelve times less than a second apart. Wait one to two second and hold down the feed button until the Column Emulation receipt prints as shown below.
To select off press the feed button once, wait one to two seconds, and then hold down the feed until you get a confirmation receipt that says that the Column Emulation is set to off. At this point you can turn off the printer and turn it back on to get out of setting.