Is there any reason to suspect that an ASI (especially a non-TSO'ed one) might be more accurate in the middle of it's range?

Also, to anyone with a combo vario/secondary ASI like LXNAV V7, does the AS indicated on the V7 agree with your primary ASI and if not, which one do you trust? A sanity check on the primary ASI with a secondary instrument seems like such a good idea to me. I mean... when my ASI eventually goes broken, I want to know right away. The redundancy is nice in the meantime, especially if they agree on speed.