Air under window frame/ where sits on sill

[ThaBoom]

Hi

Our windows are about 18months old. Nothing wrong with the fitting or any condensation.
What I notice is there is a air that can be felt as you place fingers under where the window rests- above the trim. It's foamed under the trims but we no longer have cavity closers- these were removed unfortunately by a previous fitter.

I'm wondering if I took the trim off, can I lay some polystyrene or celotex piece on along the cavity- could this help?

 

[foxhole]

How can there be nothing wrong with fitting if they are unsealed frames .

 

[ThaBoom]

How can there be nothing wrong with fitting if they are unsealed frames .

I mean the windows are fitted fine as per what the fitter has said on numerous occasions- they have visited at my request to check.

They say it was installed correctly, no outside gaps are visible and cavity was foamed.

If I call them out again they will charge us if anything needs redoing. At the moment we are trying to figure out why we have this air coming through that wasn't felt in the old windows.

Question: is it possible the cavity closer was closing off any voids.