Deviation scales are proportional to RNP. Similar to ILS localizer and glide slope deviation scales, the IAN deviation scales become more sensitive as the airplane approaches the runway.
FCOM excerpt about that. It might differ though with installed options.
We do have that 400' number as well, however that is the vertical RNP of all VNAV flight operations until the start of the approach, ie. the whole descent path from top of descent until approach intercept. For lateral RNP it depends on airspace, flight regime and selected approach, but usually is 2NM during cruise, 1NM on departue/arrival procedures and 0.5NM on transitions to approach, non precision approaches are 0.15 or 0.10 depending on type of approach.