I simply don't bother with it because I don't have the space for it.
Also, the 1.2x mod to FoF chance, is that only on Frostbolt, or is it applied to every spell? (i.e., Blizzard, Frozen Orb, and Scorch too) If just Frostbolt, that's kinda stupid because you lose casts on Blizzard/Scorch too, though if you're using Blizzard during IV, you used it very incorrectly, though still, I think the 20% mod should be applied to it as well as Scorch. Orb doesn't matter as it never benefit from IV.
In addition, I think NT and LB should procc more BF since they're affected, too. Frost Bomb is as well, but because there's only one damaging tick from FB, there's not much to do to fix that. Maybe just lower the CD and Duration w/ IV regardless if glyphed or not. (Oh, did you take into account less FFBs with your no-glyph vs glyph check? That should lower it a bit more)