I would not touch the little unlabelled screw - the DSP can be programmed with a dongle to various car shapes.
Sure the dealer coded to the correct one?
I couldn't complain about too little bass on mine - tbh I am sometimes surprised how strong the glue is that holds the rear window in; as it looks like it's gonna get shaken off any second when I turn the volume up to 50%......
In case you think about fitting yourself - it's do-able but most guides out there are for LHD. They have radio unit on the right and fuse box on the left. Now the RHDs have both on the left, i.e. fuse box is where the LHD guide tells you to run the cable through. So a lot more needs to come out to put in the wiring loom. Takes you a full afternoon (the first time)!
Basically you need to get the glovebox out including trim, to get to all the screws the bezel for climate control, radio display etc has to come off, so does the trim (left side panel only) for the centre tunnel.
To comment on loosing the spare wheel - you loose the space saver. Not a big loss - I now just carry a small compressor and can of tyre seal. If I have a flat then I just call the lease company - technically I should not be fitting spare wheel to car myself anyway (company health and safety numpties). Plus a full size tyre doesn't fit in the hole in the boot anyway (great thinking VW - Where does the flat full size one go after you fit space saver???!!!).