Thanks all, I finally found a reference:
II-C-5-12 of the 9613 states:
"(the difference between the RNAV system computed path and the aircraft position relative to the path) should be limited to ±½ the navigation accuracy associated with the procedure (i.e. 0.5 NM for the initial and intermediate segments, 0.15 NM for the final approach segment, and 0.5 NM for the missed approach segment)."