I tried tackling the horsehead last night with my c11 with a f/6.3 reducer and a UHC/LPR filter from a yellow site. I didn't see the horsehead but I did see what I'm pretty sure was the flame nebula. Unfortunately there also was a lot of clouds so I only got to look for it for a short time
This is not a great filter for trying for the Horsehead. Despite its name, the UHC/LPR is a broad-band filter and not a good nebula filter. The Horsehead responds best to the H-Beta filter, but also will be notably easier to see with a regular narrowband "UHC-like" filter like the Lumicon UHC, DGM NPB, Orion Ultrablock, or Thousand Oaks OIII LP-3 filter. Clear skies to you.