I decided to change my approach to uncoupling. I had tried to use just one magnet under the track and to attempt to rely upon the "delayed uncoupling" possiblities with the Dapol Eastshunts, but that turned out to ... not work for me.

So I ripped that magnet our and installed three, one at the end of each siding. I had to lengthen the "main" siding as I needed more room to be able to actually couple the loco to the five wagons therein.

I'm quite pleased, operationally with the change. I was able to perform a Shunting without touching the wagons at any point. I had to poke the locomotive a few times on the deadfrogs.

Next decision is how to resolve that. 

Options:

(1) use a loco with a longer wheelbase / more pickups :)

(2) completely redo the pointwork with live frog points; which will mean redoing all the trackwork because these are the smallest settrack points :(

or

(3) live with the odd finger-poke reqiured on the loco...