Currently you are not able to set up min value (custom 0% of the plugin parameter) and max value (custom 100% of the plugin parameter) of your MIDI controller knob. But AUM let's you do this, which is really great and I would love to see Loopy Pro would be able to do this.
Video:
<- I could imagine that in this particular example case the plugin parameter itself is filled with rounded numbers, something like
200, 205, 210, 215, 220 etc. and not 200, 201, 202, 203, 204, etc. In this case I would expect a drop-down menu with all the numbers of the plugin parameter but I think even then you should be able to enter manually a wished number and then the next-possible number will be rounded. Let's say, in this case you enter "202", this will make jump to "200". Or if you enter "209", this will make jump to "210".
Anyway, in LP this "%" thing is too limited and not precise:
Slack-Thread: