Question on Content of NLO LHE Output

Hi Folks,

I have a question regarding the LHE output from MG5_aMC@NLO. I have in mind a simple dijet @ NLO process.

As a preliminary, it is my understanding that during an NLO computation, after a radiation phase space point is generated, the entire (n+1)-body configuration is passed to FastJet for clustering. The post-clustered objects are then checked against cuts. Is this correct, or do I have the order in reverse?

In any case, does the output LHE file contain the pre-FastJet or post-FastJet configuration? Ignoring for a moment weighting normalization provided by the parton shower, are the 3-body configurations contained in the file individual IRC-safe objects, or do some events contain configurations that would be identified as 2-body configurations if a consistent post-shower clustering were to be performed?

I want to study the substructure of R=1 fat jets. However, it is unclear to me if I should ask MG to give me a dijet configuration with loose pT requirements and small R jet definitions, or if I can ask for a tight pT requirement and a large R.

Best,
Richard