Fuse Box and Voltage Consistency Question

The main under dash fuse box has 12.68Vs coming in (same as the battery) with the key "on" but "not" having the car motor run...is it normal to have some of the individual wires leaving the fuse box to have only 12V or slightly more, while some others have the full battery voltage..for example the wire going to the coil/fuel pump has 12.3V and does not increase that much more when the alternator provides the power