Yes, some of this is about trying not to get outflanked by Moktada-al-Sadr, ie. intra-Iraqi Shi'a politics and such, and so more by way of rhetorical posturing. But only to a fashion. If Israeli action in Lebanon lasts weeks more, rather than days more, and especially if there are more Qanas, the risks of resurgent Shi'a insurgent activity in Iraq against US forces may well rise materially, quite apart from the already dangerous dynamic underway between US forces and some of the more radical Sh'a militias. That is to say, Sistani will feel compelled to denounce the Israeli offensive in increasingly strident fashion (despite his quietest roots), and that will likely lead to consequences unhelpful to the US war effort in Iraq.