I am afraid the chances don't work like that , when we talk about the 5% success rate for example on the lvl6 box it means everyone that try to enchant such box has a chance of 5% to lend a success and 95% to fail so statistically speaking from 100 people that will try to enchant such box 5 has the chance to win. It is not bound to the boxes number as it is bound to the rate that certain box have to success or fail.