cells in the middle do not express the protein

[Eric H. Mercer]

      Hey, I've seen this too, over the last six years of transfecting
beta-gal plasmids into various cell types.  I almost exclusively use CaPO4
transfection.
I add the DNA ppt in 1 ml to 9 ml of medium already on the plate and mix. 
The
ppt. shows an even distribution, so I don't think we're necessarily seeing
an
artifact of liquid accumulating at the edges.  Any insights out there?