Yeah I'm with Macbow. Trapping really only works if the limb has some decent thickness to it.
NArrowing the limbs can drop the weight alot on a recurve. As long as you don;t make them so narrow that you lose stability.
I probably wouldn;t go any more narrow than 1.5" at absolute minimum.
Regarding trapping, for wood, always trap the back if trapping, aside from very rare exceptions.
Regarding trapping for glass, as Canopyboy recently showed, glass is stronger in tension than compression like wood, so also trapping the back is the most appropriate method, although glass is very strong so probably either will work and not cause a bow failure.