I don't believe you can set a column width to exactly 14.25, to be honest, not even programatically.

Even though Excel shows you widths such as 14.00, 14.14, 14.29, 14.43, 14.57, etc.., what you're really doing is setting the column width as a number of pixels.

14.00 = 103 pixels
14.14 = 104
14.29 = 105
14.43 = 106
etc..

My guess is Excel won't allow you to set a column width using a fraction of a pixel (makes sense), which 14.25 would be when converted to pixels.