Q-BRIDGE-MIB representation of ports on Dell PowerConnect 6248

I have a Dell PowerEdge 6248 with a 2x10Gb uplink module. I'm trying to make sense of the representation of the ports from the following snmp output:

Q-BRIDGE-MIB::dot1qVlanStaticUntaggedPorts.4081 = Hex-STRING: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

That hex string is 128 hex characters long. Each hex character represents 4 ports on the switch. Now, as it's a stackable switch I believe Q-BRIDGE-MIB contains the configuration for all units. This is where I get confused - the manual says a maximum of 12 switches can be stacked together, but:

(128 * 4 ) / 12 = 42.67 ports if the hex-string represents 12 units, or

(128 * 4) / 48 ports = 10.66 units if I am correct in assuming the hex-string represents 48 ports.

Can anyone clear up the confusion? Is my assumption that any of the 48 ports on the front can be used for VLANing not correct?

Thanks!