The fx120 has points of contact. Middle rear, and 2 adjustable feet in the front. i have found it to be sensitive as well, but easy enough to level on that chunk of granite.I ordered an FX 120i a couple of days ago and I was also thinking about the size of the base for it. My current scale an EJ 123 is extremely sensitive to adjustments so I use an 18"x18" piece of countertop for a base. Then I drilled a screw hole at each corner for a screw and I do the final adjustments with the screws. I hope I can do the same for the FX, just a smaller base.
I found mine on eBay for about $80. It was used for leather working.The people around here really think highly of their granite. I tried to get a square 2" thick for the present scale and the cheapest I could find was almost $200!!
I bought a surface plate (2" granite slab) from ENCO on sale - the shipping cost more than the plate. I pays to Google and look for the lowest price.Check amazon for a class B surface plate , i believe they are 3" thick, i just seen a video of one on the Winning in the wind youtube channel by a member here.