Having remembered the instruction in the final details, I'd diligently spotted the line in the descriptions telling me to use a crossing point. I decided the southern crossing point offered a nicer route into the control, and set off accordingly.
I tend to focus on contours when making route choice decisions on open fell, so I didn't notice that there was another substantial - but not overprinted - wall between me at the crossing point until I got to the top of the hill and saw it, and then had to swing around to the northern crossing point.
If the wall had been overprinted I wouldn't have had a problem - and, being honest, I'd probably have been fine if the line had just been bent via the only usable crossing point on that leg - but as it was I wasted 30 seconds and felt a bit grumpy about it afterwards.
(I didn't at the time spot the mapped-but-not-marked stile next to the ruin...)
It might just be me, but personally I find it difficult to spot thin black lines when trying to plan routes in race conditions (and this was with an enlargement to 1:10k!). There's a reason why we don't just use similarly thin black lines for impassable boundaries on sprint maps.
RJ wrote:It is not necessary to obscure anything on the map when you show boundaries that are not-to-be-crossed. In OCAD create a new colour (Purple or Magenta) and place it in the colour table below the Black that is used for walls, fences etc. Then create a line symbol of sufficient thickness to do the job, assign the new colour, and it will sit neatly under the wall.
Note the ISOM2017 makes it clear that this is the correct approach - the symbol for the wall or fence (or whatever) must be visible through the overprint.