51jay it appears from your picture that you are limiting air due to the position of the plate being quite low down near the front bar and possibly deflecting air upward, this may be paralax error from the photo so i apologise if you have taken offence.
i know there is a rubber seal under the bonnet as you clearly stated but the position of the plate seems to be reducing airflow to the top half of the radiator and affecting the cooling.
recently i have built a full undertray to seal up all around the radiator and IC. (mine had been carefully cut away?!?!) i also sealed the sides, so i have been looking at the top pretty closely too, haven't done anything yet so i am interested in other opinions on this topic.