The example familiar bond powers presented in the core book on page 105 all use touch range, even Razor Sharp Claws which doesn't involve both of the bonded entities.
None of the powers have any penetration listed for them nor do they talk about the need for penetration.
If we stick to range touch as the required range for familiar powers, I think we need to say that they do not require penetration to effect the familiar or to effect the magus/maga. If we don't, we wend up with the situation where a magus learns a new rank of mentem and suddenly his ability to mentally communicate with his familiar no longer functions unless he suppresses his parma.
it seems likely that this was merely something that was overlooked during the creation of the rules and could be reminded by an errata (this would make several Published familiars such as Aurulentus' Zeno the tortoise, Conscientia's Aureus, and Hugh's Bathild make more sense without requiring the familiars to intermittently suppress their resistance at unusual times.
Is this someplace in the rules already where I haven't seen it ? Do you think it is a good idea? Shall I send the idea off to David?
To me it appears to be obvious, that the powers in the bond proper defining the magus-familiar relation are even closer to both familiar and magus than each other's spells and magical abilities. So bond powers are neither resisted by both. Just that this is indeed not yet explicitly stated.
The only time I see familiar bonds getting interesting is when either the magus or the familiar are under the effect of someone else's magical resistance, such as when protected by a third party's parma.
In such border cases - where a bond power needs to overcome interfering third party magic resistance - you can give it a penetration equal to the bond strength [ArM5 p. 104].
It might also make sense to give a familiar under the bond power Razor Sharp Steel Claws [ArM5 p.105] this penetration to overcome Magic Resistance of the target of its claw attack.
But neither of this is written up explicitly.