Is this a matter for Tech Support or can someone on the forums tell me...

[Keith_K]

I've done the changes you suggested to the lines in the walls (making them solid colours) and have also changed the gravelled area to transparent for the time being.

The difference in the delays is, however, sadly infinitesimal - just a second or two.

I raised a ticket with Tech Support on Sunday and included a zipped copy of the plan but haven't had a reply as yet. Maybe they'll come up with some other suggestions. Maybe.