How old is your pan? That might make a difference, although that .25 inch isn't very much.
Could you give the cake mix maker a call at their toll free number?
One thing to consider is that cake mixes used to be 16 ounces and they, too, have shrunk as many other food products have shrunk. If the mix is less than 16 ounces, you may be safe with the smaller pan.
Putting a liner or tray underneath on the lower rack is also a good idea as previously mentioned.
Hope it turns out great!