If your poly density is violating the max limit then adding more
won't help. But it would be unusual, other than in a bed of POP
caps or MOS caps, to see this happen. Unless the upper limit
is stupid low. And if you believe so, you might challenge the
foundry as to why. You'd think a flow would be decently
producible over a 10-90%, surely 20-80% fill range amd I am
used to seeing minimum density limits below 5% and usually
none for max, because it's practiclaly impossible to hit a max
density (in terms of producibility) in any sane useful circuit
layout. Other than maybe slabs of thick metal in power ICs,
and even there all I've seen is slotting rules, which in effect
set a max density of 90% or so (30um max metal, 5um slot,
as an example).