Okay, figured it out. The prescribed mix is just too stiff and sandy, both to work in such thin/narrow layers and to adhere to the floor, so after some experimenting I came up with the following -

1) Sponging the surface with some water, as suggested on the packet, didn't help adhesion. Putting a little cement on the area, making it pasty by using fingers to sprinkle some water, then filming it over the prescribed area, did work.

2) Ignored the prescribed mix and went for 5 cups of cement to one of water - then added drops with fingers as necessary while working it into line shape.

3) Once roughly in place, sprinkled a few more drops of water up and down the line to give the surface a slightly creamy feel when running my fingers up and down the line. This helped enormously in screeding it without having it either stick to the wood or come away from the floor in clumps. Left it with a reasonably decent surface. Once dry, I'll check each one again for level and touch them up as needed.

Tedious I know, but when you're a complete dufus with cement you have to figure out some way to tame the beast!

Oops - my bad. This was supposed to have been tacked on to my other post. Thought that it was odd to be asked for another header!