Incidedentally, you said that there are published criteria as to under what circumstances a RAS will, or won't, be granted. Where would I find those? - it would be worth knowing for en-route planning.
The only place They're published is in each units MATS part II (the individual unit operating instructions). However, if you've got access to approach plates where the 25nm MSA (top right hand corner normally) is published then take the highest figure on there and you won't go far wrong.