Snipped

To "transpose that onto the coving situation" - just work out how the
mitres would have gone had you been putting up all the coving from
'scratch' and that will be the 'cut'.

*Tip* - if you have a spare length (or two) of skirting board or
similar with any type of mould on (from a simple round edge to a
complex moulding), then use that to practice on as the method will be
exactly the same.
Best of luck with the job

Cash

GMM,

To add to that, if you can pop into the likes of B & Q (or even Wickes) and
pick up a length or two of their cheapest coving just to practise on - then
that would be even better.

Cash

(Who pressed the send button before he finished the last post) :-)