Personally I wouldn't do that. Global should always be left on normal and that's the filter that will be applied to every object in the radio unless you go in to a system and change the filter on each site or in the case of conventional channels going into the department options and changing the filters for conventional objects.
So by turning Global filters off you've affected everything you're going to listen to on your radio, you may notice some differences. Without getting into all of the systems and all of the sites that your radio is programmed with and looking at them and doing a tutorial on filters here you may want to Google or search SDS filters.
Avoid the auto filters as they will slow your scanning way way down, they sample each filter and you never know which one does the trick. Sometimes turning filters off on a particular system helps. It's different for every radio in every location, what works for me won't work for you as it depends on your area interferences.
Once you start fussing with filters on particular sites of particular systems it's a good idea to add the filter indicator to your display so you will be able to tell what filter is on a particular system just by looking.
Didn't really want to get into filters before but of course that is one way you can improve reception on simulcast sites. There is an endless amount of information on the filters, unfortunately a lot of it isn't really totally correct but you might find a number of posts that I've written regarding filters.
You're going to find that filters are more of a troubleshooting tool rather than something that has to be applied to every object. Global filter is on normal for a reason, it's a good starting point, read up on your filters and go into the systems themselves and change or play with filters right on the sites of the systems.
Global is a quick and easy way to play around and now you've discovered that one system works better with all the filters off on the sites so I would simply put your Global back on normal and go into that system that was helped and turn off filters on any sites you have enabled. You will get the same effect that helped that system without removing normal filter from everything else on your radio.
There is so much information on the SDS radios just by Googling or searching the RR site.
It's late, if I had more time we would look at your systems, check out how many sites you have enabled, maybe try to isolate it to a smaller number of close sites. I would do a short tutorial on filters Etc... It's late and I'm going to bed.
Read up on the filters and enjoy!