Do you have the FOV slider mod installed (http://www.nexusmods.com/newvegas/mods/55085/?). If you do, go to its MCM menu, find the fScopeScissorAmount setting and set it to 0 there. The problem should be fixed.
In fact, I'm pretty sure you have that mod installed but you probably didn't know that it has the ScopeScissor setting too, because this happened to me. It overrides the .ini settings and causes the problem.