I use a 2" CLS CCD filter in front of all other filters on the coma corrector.
I have LRGB Ha 2" filters.
I find that it's good to just leave it there as
it also protects the inside of the filter wheel from dust.
If I was imaging outside Melbourne at a dark site I would take it off.
see here:
https://www.flickr.com/photos/247194...in/photostream