You can't compress something that is already compressed. Any further compression applied will increase size because of adding headers and hashes and the data will stay the same.

It works properly for single calendar.

You can hide certain characters using "*" in the DisplayMask. For example: 
Mask="####" 
DisplayMask = "**##"

If the value is "1234", after blur it will look like "**34"
The same approach can be used for all mask parts. The only requirement is DisplayMask to be longer or equal to the Mask. For example:
Mask = "<1..999>someLiterals####SomeMoreLiterals<3..123>"
DisplayMask = "***someLiterals**#*Some*******s<1..99>*"
If in the above example the DisplayMask is shorter or does not contains enough asterisks to match the editable parts, the visible value on blur can be wrong.