You can if need be try a slightly shorter port and part plug it with rolled resistive open cell foam. This effectively makes the port narrower, but retains the bass tuning.
This kind of stuff: https://www.ebay.co.uk/itm/ACTIVATED...1GSjecLSvo5V3Q You may find it cheaper elsewhere.
It would be trial and error though. i.e., how much to shorten the port and how tight to pack the foam. Obviously not so tight as to stop air movement.
Hope your ears are good enough to judge what goes on!