How can I set a pass limit above which is a fail?

I am creating a screen cast assessment, where I want to the learner to pass on how accurately they’ve remembered a set process. I have one ‘correct’ click box per screen which is scored to a variable called click_counter. To capture random clicks I have a further click box which covers the entire screen beneath the ‘correct’ click box. This box is also incrementing click_counter.  I have successfully set up custom result screen which go where they should depending on accuracy, however, the problem I’m encountering is that the pass mark in quizzing will not allow me to set a ‘reverse’ situation where the minimum score is a pass and the maximum is a fail (minimum indicates accuracy – maximum indicates random clicking). This obviously means that the pass or fail is will be incorrect. How can I overcome this?I’ve been going around in circles – I’ve a suspicion I will need javascript and unfortunately I’m no expert!