As an example you've show the 99% option,
but is it possible to enter 100%, without allowing to enter 999%
No it is not.
You may create a separate event to handle the proper calculations.
I ran into this case as well, but eventually decided not to use masking in this situation.
However, you can mask in this situation by allowing to left pad with 0's:
Here is quick jsfiddle with the example in action.
Right now we're limited to fixed width masking. @FagnerMartinsBrack suggestion of adding validation is the route is correct.