Subwoofer orientation

Hi folks,

I have two subwoofers (10" drivers) laying on their backs close to and facing the ceiling.
Would the weight now bearing downward affect excursion?  

I even went over to each one and flipped them upright to check for any sonic differences.
Could not notice any changes but I am still quite new to this hobby.  

It seems to me that overall output level would decrease given the extra load on the motor along with time alignment and decay issues.

Has anyone tried this ceiling facing vs normal orientation and heard/measured changes?

Would the downward bearing weight affect the longevity of the drivers?

Hopefully this is ok. With another two subs on the floor, the sound is absolutely amazing!

Thanks!