Industrial metal detector with LDC family

Although I opened a thread asked about it, I open this thread to avoid mixing questions.
We wanna design an industrial metal detector for under coveyor belt placement and i have any questions. The detection coils will be 2 sizes (160x600mm and

160x800mm).

1- With LDC1000 i can detect L (metal) and Rp (type of metal), and with LDC161X i can detect L only. Is this correct? On the other hand, with LDC161X i can get

more detection range and it can drive a lower Rp coil. It is not an absolute requirement, but I would detect type of metal.

2- What kind of coil can be better, PCB or air wire coil? Or 1 rectangular coil of 160x600, multiple array of 160x160 coil....,  I hope I explained correctly.

3- Can the mechanical enclosure be metallic (the coils are placed into the metallic enclosure, with open aperture on top of the enclosure) or not? If i put a ferrite

sheet under the coils to improve detection range?  

I have a LDC1000 kit and I´m waiting a LDC1614 kit + LDCCOILEVM for testing, although I have to make my own coils.

Any suggestions would be welcome.