Can IC-rated recessed lights come in contact with sheet plastic?
Go ahead, although I'd stick a thermocouple up there and double check the temperature to be sure
NEC 410.116(A)(2) permits IC-rated recessed fixtures to be in contact with combustible materials in the manner you describe:

(2) Type IC. A recessed luminaire that is identified for
contact with insulation, Type IC, shall be permitted to be in
contact with combustible materials at recessed parts, points of
support, and portions passing through or finishing off the
opening in the building structure

As a precaution, though, I would use a cheap type-K thermocouple probe and meter to measure the temperature at the light-to-plastic interface after the light's been left on for a few hours -- anything under 90°C should be fine, as per NEC 410.115(A):

410.115 Temperature.
(A) Combustible Material. Luminaires shall be installed so
that adjacent combustible material will not be subjected to
temperatures in excess of 90°C (194°F).