Mine have similar gaps at the top.
Were I of a cynical bent, I would believe that the gap on the top is DESIGNED to allow the accumulation of assorted 'stuff' near the bottom of the guard, such that it ensures the owner eventually notices it's time to open them up and clean the windows. Of course on my rig, the front windows are in the bedroom area, and as such, the curtains are always drawn, and I never have any idea how much 'stuff' has built up.
Reality: I know it's full of 'stuff' in there, and it's on the maintenance schedule for this fall/winter cleanup cycle, i.e. when the weather is nice and I have time...
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.