@Darrel,
From reading your answer again, I understand that the elevation antenna pattern is correct in the Datasheet, this was the first thing that I confused being wrong. In that case, positioning the R550 on the ceiling pointing down to have coverage towards below is not a good option because the antenna pattern in the elevation looks to have almost distributed coverage over and below the unit, as is not the case with R310, R320, R510 and etc... which are oriented to cover over the top of the unit. In my case at home, replacing the R320 on the ceiling on the last floor with R550 offered me worse signal than before, especially on the 5Ghz band. R320 and R550 are having similar TX power and the R550 have slightly better receive sensitivity comparing 5Ghz VH80/MCS7
