Hi
The range (-10V to 10V) you are seeing is the range of the AD-Converter of your board, not the one of your FT-modul. (The FT-Modul has no range settings). You have to set the input limits in your SW environment. If you set the input limits, than the best gain which your board provides is applied. See this link to see how it's working in LV.
http://digital.ni.com/public.nsf/websearch/CBA83550AB782D1C862566210061BEB9?OpenDocument
Hope this helps
Luca P.
Regards,
Luca