I have no doubt this is the set of standard response but they strike me, a non-user of multi, as a counter productive. I say that because I think the 3♣ and 3♦ call are subject to giving the opps useful calls when you have the worst hands rather than the best. The 3♥ and 3♠ are at their preemptive best when the opps get no other useful calls than what they already had. Plus IMO this helps your partner screw with the opps to your best advantage.