Are you not worried that somebody stepping into your passenger seat might break the speaker grille?
Having the seats being so low, and sometimes not being able to fully open my door (due to other nearby cars), I always step really hard into the passenger footwell area, before I am able to sit down.
That foam is there also for this specific reason, and now, being thinner...
The speaker is also now covered with the remaining foam, doesn't that affect the sound quality?
Also, did you consider putting the base into the trunk? Possibly into the spare wheel area?
Not sure how it would behave with the top down, but while the top is up, I think the trunk space would further amplify the sound quality.
I have also previously seen most people add their base system in the trunk for this specific reason.
I have retrofitted OEM Bose system into my previous R170. The placement of the additional speakers were on the back wall, just behind the seats, and the sound faced the driver/passenger.
I am no sound expert, just my 2 cents