Typically you would size the t-molding to fit it.
for instance if using 3/4" t-molding, you can build you cp top out of 5/8" mdf and then lay you graphics on that, and then cover it with a 1/8' thick acrylic to protect your graphics. The 5/8" mdf added to the 1/8" acrylic will equel the 3/4" of the t-molding.
you can also get other sizes of t-molding if needed. you also use a size that is wider than needed and then trim it to size.