Hello,
If both switches have the same priority set their MAC address will be the tiebreaker so if switch B has a lower MAC address that will win the election.
The bridge priority (if extended system ID is enabled) is built up from 4 bit priority and 12 VLAN ID.
Therefore the Bit 16, Bit 15, Bit 14, Bit 13 have the values of 32768, 16384, 8192, 4096.
I think the 8192 for secondary and 4096 for the primary would be OK.
Hope it helps, rate if does
Krisztian