Elevation will affect your external ballistics and may get you closer to a more acceptable stability factor, but I doubt it will change your group size to a large extent. What distance are you shooting (assuming 100 yards).
I've shot several bullets that were marginally stable (1.26-1.31) and not had any issues. If your third shot is always opening your group, it's likely due to heating of the barrel. Try letting it cool longer between shots, or try another bullet and see if the same problem persists.