Custom monitor, how to select one instance value from "get bulk"?

Custom monitor, how to select one instance value from "get bulk"?

I have a custom monitor which uses an SNMP "getbulk" for table entries which returns enumerated values (i.e. OID.1, OID.2 etc.), the "test monitor" function in edit monitor however times out with"Monitor did not respond to the test request"...
 
Running a packet sniffer on the same server interface as the OpManager server shows the SNMP requests go out, and the replies with data (all 10 enumerated responses are present with sequence numbers all equal to the request sequence number).
 
How do I get OpManger's custom monitor to filter on the enumeration (e.g. OID.1, OID.2) and display the data contained in the relevant response?
 
OpManager version is 11300, end device being polled is a Meinberg M600, firmware 6.17.005, the Meinberg LTNG-MIB mib appropriate to the device is loaded with all supporting Meinberg and RFC mibs.
 
Thanks for any help!

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