There is potential for greater differential movement as cavities widen between a timber inner leaf and a masonry outer leaf.
This is because of the see-saw effect wherein upward or downward movement becomes more pronounced as it becomes more distant from the notional central pivot point.
The Type WCA Cavicloser (Wide Cavity Applications) uses ties to secure into the masonry outer leaf whilst fixing into the timber inner leaf is mechanical via the friction-fit side section which benefits potential drying-out movement provision.