72 drops each of sensitizer and metal for a 12x20 on platinotype sounds
like an awful lot for glass rod coating.
So maybe cut back to 3/4 that much and see if you can get a smooth
coating. Next try some Tween 20 (one or two drops of 20% dilution should
be about right) this seems to help smooth the coating and absorbtion on
platinotype, though doesn't work equally well with all papers. Finally,
your technique with the coating tube may be improvable. Even if the
paper buckles a bit, you may be able to maintain full contact by moving
the rod *very* slowly, slower with each pass across the paper, and using
very little pressure, maybe just the weight of the rod itself. Or, if
you've got a good strong coating on the paper when you "lose the bead"
off the coating rod, just make a last pass with pressure, using the rod
like a squeegee, and mop up any excess liquid at the edge of the print
with a paper towel. Hope some of these ideas help.---Carl