MegaWizard Altsyncram generated component uses more M4K blocks then reported

Let's leave the binary boundaries aside for a momemt. Life isn't always that simple ...

Actually in x9 mode, it 4 M4K should hold 768 24 bit words.

The question was: why does the fitter use 5 M4K if the MegaWizard reports it can do it in 4?

I the depth is limited to 256, the MegaWizard also reports 4 M4K used but about 50 Lut in stead of about 20 for the depth of 512. If we leave it Auto, it will use 6 M4K (in 2048 x 2).

By the way: the design is 106% full (after Analysis and Synthesis). I already have a few logic-Cells based dcfifo I'd like to replace with the free M4K blocks.