Lindsay,
Due to the fact that the leaf is positioned in a way so that it is biased toward the slotted foam on the lid it leaves a larger gap for the wings of the flies placed in the bottom of the box and this is where I place my overly delicate stuff.
As the box hold something like 940 flies, well at least has this amount of slots, then removing the leaf and leaving 2 spaces between flies still allows you to have more than enough fly patterns & in various sizes to cover eventualities.
Iain