To say anything a SNMPwalk of the device is needed.
Or better said the part of the snmp data that is used by the check.
If i look at the MIB file for this device then i see that an extra table exists for internal sensors.
→ .1.3.6.1.4.1.21239.5.1.2.1.5 (Internal Temp) and .1.3.6.1.4.1.21239.5.1.2.1.6 (Internal Humidity)
The original check only used this internal table.
I would recommend to use the original check and make one extra check that fetches the external sensors only.