The terminals have nothing to do with the size of the icon - they are defined by the connector pattern you use. If you want an icon about the same size as a numeric, select the pattern with 2 connectors on the left and 2 on the right. Assuming you have a single input and a single output, connect them to the uppermost left and uppermost right. Now, when you go into into the icon editor, select "show terminals". Draw a box the same size as the connector pattern you're wired to. Make sure you have the same icon for the b&w, 16, and 256 color.