# How many resist chances does one get against Mental Manipulation spells in SR5?

I am trying to understand how resisting Mental Manipulation spells works. Let's say I have a mage (spellcasting 6/Magic 6) casting Influence (drain: F-1) on someone not half bad (W/L 5/4, initiative >10). Until the spell is permanent, I have to uphold it for F combat rounds, the target can make a resist roll every action phase. So lets say I cast at force 4/6:

I get 3/5 points of drain (easily resisted versus some potential for headache)

• I can get up to 4/6 successes with 12d
• The target gets -4/-6 on all (subsequent) rolls to shake of the spell
• I need 4/6 combat rounds of upholding the spell
• The target gets an initial 9d to resist
• Every action phase (two per combat round?) for 4/6 rounds, he gets another 5/3d (W+L-F) to shake of the effect
• -> that is 40 (4*2*(9-4))/36 (6*2*(9-6))d to shake off the effect (plus another roll whenever he notices something wrong with the suggestion, but that seems rather minor in comparison)

Unless there is some major flaw in my calculation it seems almost impossible to make Influence stick on a target, unless the force is above their W+L, so they do not get any further rolls, but that means major drain potential.

Or is it that the target only gets to make a roll to shake off the spell, if he notices something going on? And is it the same math Control Thoughts/Actions? At least I can make them do stuff while they're controlled, although I would prefer the more subtle approach of Influence.