either flow or lighting the mesh does block some light, if you use a deeper container like s specimin container you can usually leave the mesh off the top as long as flow isnt going to lift the frags out of the container, I use one with holes drilled through the sides to allow flow but not enough to blow the frags out, with no mesh over it. I hope this helps you out a bit.
another method that works great with leathers is to place a rock so its touching the mother colony, the leather will attach eventually (give it about three weeks so it has a good purchase on the rock) then cut free the section attached to the rock. You can also do this with rics and shrooms, this is a veryu slow method of fragging but often a higher success ratio, it may work best for you if you are having trouble fragging by other methods.