Yes I am concerned about the 143 reserve. I've talked to three experienced jumpers on my dropzone separately and they've all said it's fine. I will probably try to get the Optimum 160 reserve, I'll be wingloading that at 1.25. Not perfect but manageable I suppose? The attitude at my dropzone is that since it's a reserve ride as long as it saves your life it's okay and it flies docile because it's a 7 cell.
Again I'm just a newbie so I don't really know much.