Penetration for Entrancement and Related Abilities

I was wondering if anyone could help me.

I'm a little confused about how to calculate penetration with Entrancement and related abilities. My problem stems from the fact that, as I understand it, there is no Ease Factor making it impossible to use the Casting Total – Ease Factor formula normally used for supernatural abilities. Instead, the caster apparently rolls Entrancement + Presence and the target rolls Stamina + modifiers with victory going to the high roller.

If the Entrancer wins, the result of the Entrancee's Stamina roll could then be treated as the EF for the purpose of calculating penetration. However on page 65 of the Core Book it states that:

"Hermetic Magi get their normal Mentem Magic Resistance, and get the normal Stamina roll if the effect penetrates".

Which gives the impression that the Stamina roll comes after rolling for penetration. So perhaps you apply the entire Casting Total to penetration then, if it penetrates, the magus can roll Stamina to resist as normal.

Are either of these theories correct?

I'd wager that this statement:

is a relic from an earlier draft/eddition where folks got a great number of resistance rolls against spells that had already penetrated their magic resitance. I would use the mentem bonus for rolls such as those required to notice the effects of "recollection of memories not quite lived" and "loss of but a moment's memory".

For penetration I would have the character make their resistance roll (mentem bonus included) and then see if the entracer exceeds the resistance roll by more than the target's magic resistance.

Make the resistance roll to set the ease factor and then determine what happens.

What I'd do:

The player declares his intend.
Then, it's Dice roll - MR, and see if it is enough for what the player tried.

So I wasn't misreading anything. Thats somewhat of a relief, I guess. But, now I've got to choose how I want to do it.

To make things even more confusing, I was rereading the section about designing Major Supernatural Virtues in HOH: Societates in the hope that it might give some insight. Fortunately, it was one of the examples used. It says that the effectiveness is based on the Casting Total achieved.

So that seems to be yet more evidence for the MR+stamina+modifiers+die roll = ER Hypothesis. This gives roughly a EF 13 to affect a typical starting level magus, or 8 to affect someone without magic resistance.

This seems reasonable. I'll give it a few tries and see how things go.