You programmed CV56.26.0-1 correctly for 56.0 inches.
The readout problem was because you programmed CV56.26.0 first, then CV56.26.1.
Note the following from page 359 of the DCC Ref Manual version 5.1.1:
"If Programming Verbal Acknowledgement is enabled (see CV62), program CV56.26.1 first,
then CV56.26.0. The locomotive reads out the two byte value when the low byte is programmed."
When you programmed CV56.26.0 = 226, CV56.26.1 was still the default 26.
The verbal announcement corresponded to 26 * 256 + 226 = 68.8 inches.
To have the decoder readout the current CV56.26.0-1 value,