old system---
used to have a placard, to maintain minimum 45% N1 in icing conditions to prevent the ice from going into the core--newer engine mods automatically raise the idle when anti-ice and ignition switches are on, in addition to the redesign of the cone on the fan. we called the different engine cones--Dolly Partons (rounded) or Madonnas (pointed)
whichever mod your aircraft has, should either be placarded to telll you to keep 45 N1 or not.
so must have been the same idea for the heavy rain--to propell the heavier rain drops outward away from the core.