FPGA input capacitance
Most of the capacitance comes from the packaging, and then from the gate/drain/source capacitance of the transistors. I don't think anyone but the manufacturer will be able to narrow the range for you. Someone on the internet may have anecdotal numbers to offer, but the manufacturer is free to change the package or the process at any time as long as the part still falls within the specified range. If you only need a few parts, measure the capacitance yourself.