I think the issue isn't to do with how much the directors are...

I think the issue isn't to do with how much the directors are about to sell. It has more to do with the fact that the change in policy has eased the restrictions placed on them, thereby making it easier for them to sell going forward. After reading the AFR article, I compared the new and the old Trading Policy documents. The key change is outlined below:

Previously, the blackout period (where insiders aren't allowed to sell) was from 1st July / 1st January, till such a time when the company lodged it's full year and half year results respectively. Under the new policy, the insiders don't have to wait until lodging the full year and half year results. They can sell down after TPW updates the market with un-audited EBITDA figures, which can be provided to the market far sooner than the final result (that is often lodged in August and Feb/March).

Given the change, I expect the company to provide the market with the full year un-audited EBITDA figure along with the latest quarterly. This has spooked the market because investors think that there is a high likelihood of director selldown also occurring at the same time. Anyway time will tell what happens...