My car has very big opening in door panels. Like nothing on inner side. I covered them with big sheets Dynamat. I feel the bass is muddy and not much tight. How to improve it?

https://reflectology.co.uk/wp-conten...723_165851.jpg
(not my door but same model.)
Equipment:
Head unit OE
Helix P Six MKII (Helix DSP2 and Zapco 6ch AP are going in.)
Sinfoni T25T
Scanspeak 10F
Sinfoni T165W
ARC Black 12" IB (Zapco ST-500XMII 300watt)