The Koksijde CTR might also be active, but to a lower limit that's depicted on the chart
Any sources or references for this? I've never heard anything like this, not for EBFN neither for any other Belgian a/d. Belgian AIP is brief and clear: "GND-FL55" and that is that.
And, in my experience, Koksyde will very rarely be active during weekends - though of course, NOTAM's must always be consulted.