https://www.boeing.com/content/dam/b...r_3.pdf#page63 I didn't find it in the FCOM but this document indeed contained very relevant information.
Page 63, 5.9 meters.
Hence I computed 15.4 meters.
Then upon landing : (5.9+5/57.3*34.85)/tan(16/57.3) = 31.2 meters.
It's a bit disappointing. It doesn't explain why we think we landed much further than we actually did.