Just read the T&Cs, which say that this is only true for Golds.
Silvers can only buy 1000 Tier miles and Blues can't buy any.
That seems to fit the logic of a percentage of the original total required. The relatively low numbers also suggest M&B is firmly pushing members towards flying with them, and therefore in almost all cases boosting the Greek economy, in order to re-qualify.
Blues were never slated to have the ability to buy miles.