prpmernel:
the EZE flight in question was at FL185. The clearance to join at NEW was for FL180 and then route towards HAVEN
So Scottish gave him a clearance to "join" at NEW at FL180. Join what? FL180 at NEW is outside CAS (he'd have just left it). And given that he was outside CAS and Scottish had refused him anything better than a FIS outside CAS, did he still get only a FIS on this extended routing? Presumably the reason they did not give him FL220 from NEW (to keep him inside L602) is because he couldn't get up to FL220?
As for alternative routings, there are two routes suggested by the Standard Routes Document when P18 north of NEW is not available. One is NEW DCT SAB DCT ADN - "this route may be filed by traffic that wish to seek ATSOCAS from Scottish Military". The other is to POL then airways all the way to Abdn. The difference in track mileage surely can't be so big that it makes it much more acceptable to take the extra risk.
NS