You can try that... but I wonder if the plugin itself has some sort of control to try and get rid of unexpected data?
Unfortunately, Adobe's plugin code is rarely readable by humans.... so I am not sure off-hand if this is the case....
If you are on a dev environment, you could try adding a custom code block before your adobe stuff that does the following:
console.log("!!!!!!!!!!!!!!!!!!! Test Highest % Viewed !!!!!!!!!!!");
console.log(window._ppvHighestPercentViewed);
// add in any of the other plugin calls that you may want to test
This should print into your console some information about the values right before your tracking fires... see if you can spot anything strange there....