I would definitely lower your mash temp and/or add the sugar to bring that down. 20 is a bit high for a IIPA. however, higher fg's are supposed to help with head retention.
the carapils and sugar are definitely conflicting qualities but sometimes it works (see Pliny the Elder). there are lots of factors that effect your head stability (hop rate, yeast strain, beer temp, ferm temp, FG, CO2 volume, malt type, abv) so seeing your recipe might help figure out what to do.