Clearance for 4" door speakers in the F22 and across many BMW chassis codes is ~42mm, and I believe there are some 4 door BMW models that may allow a few more mm, not sure on that. There are a few aftermarket BMW specific retrofit 4" drivers that fit (Eton and Bavsound comes to mind) and a few other mainstream aftermarket vendors that have shallow 4" drivers that will fit this spec. For example, the Audiofrog GB40 4" drivers will fit perfectly, they have a 41mm mounting depth thanks to its smaller Neodymium Motor. Actually, when Audiofrog owner Andy Wehmeyer was designing these 4" drivers he had BMW's specifically in mind. But these Audiofrog 4" drivers aren't cheap at ~$450 per pair but there are more examples of really good 4" drivers, component sets, and coaxials for less. And if budget isn't a concern then the Dynaudio Esotar E430 drivers will fit perfectly as well and would be probably the best midrange driver you could get to fit your stock 4" door cavity but at around $2K for the pair, you'll have to pay to play.
But I digress, for a potential solution to allow deeper drivers, if you go with a set of PVC adapter rings from the seller "73mustangconv" on eBay, mounting depth would be increased to "50mm-52mm". I think he lists 50-52mm since these 4" adapters would work for multiple BMW chassis codes but in the listing he has a picture of a F22 passenger side door with 4" Morel Maximo coaxial installed which he notes has a 52mm mounting depth. There are two pics on the listing, one with the speaker mounted on the adapter with the door card off, the other with the door card on but with the factory speaker grill left off.
https://www.ebay.com/itm/BMW-F30-31-...cAAOSwDk5UExUe
Here is a link to that morel speaker for reference:
https://www.woofersetc.com/p-10027-m...er-system.html
BTW If you're running the factory amp I would look for other drivers with higher efficiency than those Morels. Our factory amps are already weak as it is, with 87.5db sensitivity on the Morels the OEM amp may struggle to keep up.
edit: Sorry, forgot to mention a disclaimer that if you're running the OEM amp and want to run a dedicated 4"midrange driver like the Audiofrog then you'll have to add a passive x-over to allow a seperate tweeter to be added as you only have two channels up front (left and right doors) from the factory amp. As good as the GB40's are for midrange duty, they would make terrible tweeters.