John
If the total load on this service is 225 amps you are correct 240.4(B) would permit the installation of 300 kcmil protected by a 300 amp breaker or fuse. If the calculated load on this service is >285 amps 350 kcmil cables would be required. If you signed a contract to install the electrical system according to the plans you need to follow them.
Curt
