"But...the counter argument was if we are being protected by a set number of miles either side of track, would the controller necessarily care if we were forced to deviate within that protected airspace, especially considering deviations are normally lateral and not vertical. In other words his argument is we should only ask for deviations if we will exit the protected airspace being generated for the track centreline."
In a radar controlled airspace(Radar Identified) you should always ask