Yay! Sussed it
Ive modified the track plan (again!) and moved the reverse loop, so in effect it now joins the two ends of the figure 8, if that makes sense.
That means I:
A) Save track (a LOT of it!)
B) got rid of the severe gradient that was giving me a headache
and C) can actually turn trains while they are out on the run, rather than ONLY being able to do it on the way back to the shed.
The big box of 45mm offcuts I bought 12 mnths ago has proved to be a godsend as well. Saved me a bunch of dremmel time!