Grounding Spells through Foci, Can it still be done? Options

[Mugzy]

After looking in the SR3 ruls and MiTS, I can't seem to find any instance where a mage from astral space is able to ground a spell through an active foci, provided the spell is a non-targeted, area of effect spell, and using the foci's rating as the resistance factor. Also, the Grimoire 2 alluded to being able to ground through quickened spells, as they were open "vorticies" to astral space, using the spell's rating as the resistance factor.

If I recall correctly, in 2nd Ed, this was a good reason to get masking to mask those foci, and to put a balancing factor on the quickened/locked spell guy, as it would destroy the bond between the mage and the focus, requiring a re-bonding.

I think I remember SR3 saying something about open vorticies to astral space, but not saying anything about grounding spells through foci directly.

Anyone have any info on this? If not, anyone have any house rules? All the games Ive seen about are mage heavy, and this is a great balancing factor to that, being as magic is supposed to be rare.