The picture below is my modified spoiler. The black carbon part is the new section that I added.. The bottom photo is a picture of the spoiler painted and installed on the glider. I used a spoiler off an original Atos as the template for the modified spoiler. The modified spoiler is now almost the same size as the original Atos.
The Atos-C spoilers are attached differently than the spoilers on the Atos. On the Atos-C, the spoiler are attached with two types of tape and stitching at the ends. They are first attached with a product I believe is Seamstik, or Super Seamstik available from Sailrite. This Seamstik is used to attach the spoiler to the sail hinge, then the ends of the spoiler are sewn to the same sail hinge. (I found another tape made by Tesa in Germany that is the same as Seamstik, I purchased it from a spinnaker shop) A layer of Dacron adhesive sail repair tape is place on top the the sail hinge and onto the spoiler. This will all make sense if you ever take the spoiler off.
The glider with the modified spoiler feels the same in flight when making normal turns. When I make a maximum deflection turn the glider turns much faster than previously. I talked to Felix prior to making this change. He said they tested the Atos-C with both the new smaller (now standard on the C model) and the older lager spoiler from an Atos. Pilots reported that they liked the feel of the smaller spoiler better. Felix found that lighter pilots (hook in weight around 75 Kg (175 pounds) were not deflection the larger spoiler all the way so it felt heavier to them. He said that he personally prefers the larger spoiler, but they sell most of their gliders to smaller pilots, so they have the smaller spoilers.