12.5 degrees in and of itself is not the issue, however line of sight (LoS) - which becomes increasingly more difficult at lower angles - can be a precluding problem. I'm at 20 degrees inclination for 129, but looking through trees which I have had to have trimmed twice. When the LoS is relatively clear, I get strong reception. Currently I need 129 for my HD locals. They might be mirrored on one of the EA sats. (I never checked), but even if so I also have LoS issues with the EA sats. unless I move my current dish location a considerable distance back on my property, which will involve setting up a pole mount and trenching at least 100' of coax.
When I went through this, I had a tech come out (free, since they just added the channels to 129 and I needed the added dish to receive programming for which I was already paying!) and "find" the sat. for me. He didn't think it would work but we did a "cheap 'n' dirty" 129 wing installation in mid-spring with a D500 he had with him and it did indeed work...until a couple of days later when the leaves came out on the trees. I made a simple "129 sighter" with an angle of cardboard cut to 20 deg. I taped that to a level and set it on a table on the peak of my roof near the dish location, leveled it, and swung it to (IIRC) 245 deg. magnetic (bearing from my location) using my trusty old Boy Scout compass. This allowed me to identify the interferring trees. When the tree trimmer came over, I connected a "Dish Finder" meter in line with the 129 LNB cable and listened to the tone it produces. We kept trimming until the tone got very strong. Voila! 129 reception when the leaves are out, thanks to the nice hole we opened-up in the canopy.
So feel free to experiment! Worked for me. Get your intended mounting location as high as possible and aimed correctly and you might find out you'll be OK on the LoS issue...or at least learn exactly why you don't have LoS...