Hi austra1998,
where is it written that rvr is controlling?
The gist of
http://www.icao.int/safety/meteorolo...N.011.5.en.pdf should be included in your OPS Manuals.
See Appendix E of ICAO Manual of all weather Ops DOC 9365,
"An operator must ensure that a MET Visibility to RVR/CMV conversion is not used for take off, for calculating any other required RVR minimum less than 800m (1/2sm)
or when reported RVR is available."