LHE tree structure

Hi,

I have a naive question about the truth record for some ttbar+photon events we have generated with a process like:
generate p p > t t~ > l+ vl b s c~ b~ a

The LHE files contain examples like this:

13 1 0.8345091E-03 0.1245473E+03 0.7555786E-02 0.1238767E+00
       21 -1 0 0 ...etc.
       21 -1 0 0 ...etc.
        6 2 1 2 ...etc.
       24 2 3 3 ...etc.
       -6 2 1 2 ...etc.
      -24 2 5 5 ...etc.
      -13 1 4 4 ...etc.
       14 1 4 4 ...etc.
        5 1 3 3 ...etc.
        3 1 6 6 ...etc.
       -4 1 6 6 ...etc.
       -5 1 5 5 ...etc.
       22 1 6 6 ...etc.

where the photon appears to be radiated from the W boson.

There are of course also diagrams where the photon is radiated from the leptons from the leptonic W decay, but here is where I start to get confused.... in a 5k event LHE file there is not a single case in the event record where this is shown. Specifically, I would expect to see something like this:

13 1 0.8345091E-03 0.1245473E+03 0.7555786E-02 0.1238767E+00
       21 -1 0 0 ...etc.
       21 -1 0 0 ...etc.
        6 2 1 2 ...etc.
       24 2 3 3 ...etc.
       -6 2 1 2 ...etc.
      -24 2 5 5 ...etc.
      -13 1 4 4 ...etc.
       14 1 4 4 ...etc.
        5 1 3 3 ...etc.
        3 1 6 6 ...etc.
       -4 1 6 6 ...etc.
       -5 1 5 5 ...etc.
       22 1 7 6 ...etc.

(note the 7 in the last line to indicate radiation from the -13 rather than -24)

Is this expected? I would have thought that the cross section would be comparable for events with photon radiation from the W and photon radiation from the leptons, but maybe that's completely wrong? :-)

Or perhaps this is a deliberate convention in the event record?

Any insight would be much appreciated!

Best,

Josh