My recent Aeroplan award experience is limited to a couple of tickets. In both situations, I needed to change flights and the award inventory opened up 1-2 weeks from to the flight date. Of course, as others have stated, it all depends on supply and demand so YMMV.

Have you looked into purchasing a round trip FRA-LIS to see if you get better pricing?

Or a routing with connection e.g. FRA-MUC-LIS? That’s was our award routing on the last trip..