like i said in the notes- the wording to more accurately portray the exact particulars of the mechanic sounds awkward and isn't necessary. and "up to" doesnt man "it will always be the maximum of", if someone says "you can save up to $5000 by going with our service" you'd be wrong to think "oh, theyre going to save me $5,000".
the wording on the card could either be "30% of damage" or "up to 3 damage", trying to combine the two will lack flow and be awkward. exact percents, and formulas to generate them are not uncommonly left off of cards, examples being skull shield or mutation.
if someone can come up with a grammatically correct sentence with a good flow to it that will fit within the text box and better describe the mechanic, i would be open to adjusting it. but as is, i think it is sufficient.