Hi Sean,
HttpWatch will be useless for that purpose. Why? Because it shows local HTTP traffic from your web browser perspective. MSS data fetch takes place between your backend and system where MSS application runs.
Having said that best option would be to set up a trace on the backend system to see how certain fields are retrieved.
In case of OADP fields retrieval (MSS WDA) search for implementations of IF_HRTMC_DR_FIELDS interface.