I think the quick / automatic segments based directly on dimension values are all hit, and I don't think you can change that sadly.... (you should log an idea about that!)
I generally create Segments and use those in my Drop Downs... now this will prevent the "automatic filters" based on multiple drop downs if you are relying on that... and that may be a factor for you depending on your needs.... but as I said, there is limited control on these automatically created dropdowns.
If you do want to go with creating your own segments, you should know that you don't even have to create "permanent" segments if you don't want; since these could flood your Components list... here is a little trick I have found:
First, create a new Ad Hoc segment in the panel by clicking on the + in the segment area of the panel.
Then create your segment, making sure not to check this check box:
Now, you can't drag your segment directly from the panel into another segment slot using shift, which makes a lot of people think this isn't possible...
But, here's the catch... drag the segment from the panel into a freeform table... now drag from the freeform table back to a segment drop zone in the panel, and shift will work to turn it into a drop down.