I've only used leg tendon to back bows with.  I use back sinew for any time I want longer threads.  I'm not sure 4 leg tendons is enough to back a bow.  6 might be.  I usually put on 2 layers, both at the same time, and have the second layer not go all the way to the tips.  Lately, like JW, I don't sinew back much.
George