Whats the temp outside and what kind of lamp are u using?
190cfm for extractor is a tiny for 4x4 space, u can only use it with a low led light, unless u have to take a bigger one. I use a 220/280 in a 2x4 , is a little bit overpower but i will put it at least in your box for a right air excange, not a conduct one for a good airflow through the carbon filter that will be around 400