I checked out the previous threads on focal reducer spacing but I'm not sure
they answered my concern.

I use a CCDT67 with my 10"LX200R, AO-8, CFW-9 and ST8-XME. The CCDT67-to-focal
plane distance is about 5.5 inches resulting in reduction factor in the
neighborhood of .55 and an overall focal length of about 1800mm so the SCT focal
length must be around 3200mm (vs a design FL of 2500mm). I lock down the mirror
and use a Feathertouch focuser.

The previous threads indicated the spacing (and therefore the reduction) wasn't
critical but I wonder what the effect of increasing the SCT focal length by
pushing the primary forward is. I can't seem to get my FWHM below 2.5-3.0" even
when CCDInspector tells me the alignment is good. Seeing hasn't been all that
great but the best I've ever seen is 2.5" (binned 1x1). Seems to me this is
about twice what a diffraction limited system should see (I'm in NE Ohio so I
don't expect really good seeing but this seems a bit high). I'm tempted to
remove the CCDT67 but then I'd have to refocus with the primary mirror, which in
turn changes the focal length, etc so I'm comparing apples and oranges.

Anybody have any thoughts on this - how far can you adjust an SCT (of course not
a true RC) and still get decent image quality?