If you must leave your new high performance alternator wired through the 1/2/BOTH switch then this is the correct wiring for the voltage sensing.
#1 Negative regulator or regulator B- goes to HOUSE bank negative terminal.
#2 Positive volt sense goes as close to the bank as it can be without the ability to decouple voltage sensing from the bank receiving charge current. This means the "C" post of the battery switch is the absolute closest you can get to the battery terminals and be safe.
Is this ideal? No, but if you choose to leave the alternator output/B+ wire passing through the starter cable, via the "C" post of the battery switch, this is the best you can do without toasting the start battery at some point in time.
IMPORTANT: Running a performance externally sensed alternator through a battery switch is a poor choice for a number of reasons, voltage drop and voltage corrections driving DC loads voltage too high are but two reasons why this is a poor choice. When installing a performance alternator wiring it directly to the house bank is the best practice..