Number of tucks in synthetic three-strand tapered eye splices

[Brion Toss]

Hi again,
A backed tuck is one taken with the lay, rather than against. It's the style sailmakers use, because it is more compact. If you make all the tucks this way you'll have a sailmaker's splice, of sorts. Riggers don't do this because it is less secure; sailmakers deal with this by sewing the rope to the canvas. But backing the last tuck on on a rigger's splice makes for a quick taper.
As for flattening the strands, it is always best to do so, both because the splice is more compact -- and thus more chafe-resistant and handsome -- and because the splice is more secure, as the flattened strands can generate more friction in the rope.
I believe you'll find more about these details in the "Apprentice", among other places.
Fair leads,
Brion Toss