DX, out of curiosity I checked both Lasors and JAR-FCL 1.125 and nowhere does it say straight-line distance or dogleg, as far as I can tell. All it says is a flight of 150 nm or more, with two full stops at a different aerodrome. So I guess there is room for interpretation anyway. Plus, a "reasonable" dogleg will probably not add many miles to the total so the point is moot anyway.