Only a space of 2 between screen and requested odds?

Does Bet Persistence and Keep In Play only work if the requested odds are within 2 spaces of the screen odds ?  For example  screen odds of 2 and requested odds of 4 will be left unmatched until they are matched, but screen odds of 2 and requested odds of 5 will not be placed, the Bet Persistence and the Keep in Play options will not appear.  Would be grateful for comments as to how to make an unmatched bet 0f 5 or six spaces difference stay unmatched throughout the race until it is matched, or not.