The capacity depends on what your limiting parameters are. The current capacity given by various standards will depend on the conditions that those standards assume. Electrical codes, for instance, will give different capacities depending on free air or in conduit with different conduit fill factors. Standards usually base current capacities on allowable power loss per unit length, but your application may require a different max power loss, or you may have a very long conductor and be more concerned about voltage drop. It's important to understand the conditions that the standard assumes and the limiting parameters they use, because the conditions in your application may differ substantially.
If you have a maximum voltage drop specification, then you need to determine the resistance which would, in fact, take into account the length of the conductor. However, I would suspect that the contact resistance would be a much larger factor than conductor resistance, unless your contacts have to move across a very long conductor.
If you need to determine the total resistance of a set of parallel resistances (IE, your 10-12 contact resistances in parallel), there's a simple equation for that: Rtotal = 1/( 1/R1 + 1/R2 + ... + 1/Rn ). If all of the resistances are identical, then for n resistances this simplifies to Rtotal = R1/n.