Saddle height on an ebike is more of a comfort/pain issue than a pedalling efficiency one.
But I think comfort, pain and possible long term joint damage is at least as important, if not more so.
The default position should be: 'Get the job right', not: 'Near enough is good enough'.
Thanks everyone, it all makes a lot of sense and I'd definitely go along with Rob F!
I'm not too far off the correct saddle height and am making a point of mounting and dismounting correctly - this isn't difficult to remember as once again the advice here is spot on and it is actually the easiest way.
I suspect the need to have a vice like grip on the handlebars at all times is probably just me, but once I have the saddle in the right place I'll experiment a bit with the handlebars and see if there's a height that doesn't mean I end up having to prise my fingers off them after a ride of any length!