If you can't add probabilities why are you adding P(7) to anything? Under that system 3 P(7)s would yield a probability over 1.

Alright:

P(7 cards) = .399
P(6 cards) = .3514


Probability you don't have a force in the opening grip: 1-P(7)
Probability you don't have a force in the first mull: 1-P(6)

Proability that you don't have a force in either the first seven or six:  (1-P(7)) * (1-P(6))

Probability that you have a force in either or both is the composite of this (previous + this = 1.00):
1 - (1-P(7)) * (1-P(6)).

I'm a bit late in the conversation, but this hasn't been brought up yet. If an event has a 40% probability of occuring, this means that given an incredibly large number of trials, the event will occur in 40% of the trials. 3 is not incredibly large, nor is it even close. We as humans have come to expect such probabilities to be spread out evently, which of course is a highly flawed perception.

I personally don't run more than tendrils and pyroclasm for wish targets. Remember that you're not playing keeper here; you don't need an answer to everything in play. The rebuild/echoing truth is already in the mainboard, so you don't need an artifact removal sorcery.