Getting pressurized cooling air into the front is important so sealing the entry ducting is important as having a nice big opening in the bumper. BUT Pay attention to where the hot air goes to get OUT of the car and that you have an equally sized and clear path. In a stock fd3s it actually goes into the head light area and then into the fender and out the vent in the fender!!!! If you put a big cooler in it may not have a similar sized path to get the hot air OUT! in which case you just wasted a lot of money to create a head light heater which will cook the main electrical harness in that area and headlight motor!

 

Do you have the stock undertray installed?

 

I do not recommend deleting the undertray just to provide an air path. It screws up the dynamic balance of the car and increases drag.