Manu, I think you have asked this question before!
generally, as a rule of thumb, you need to set the AVR crossover frequency according to the response of the speakers designated as "small". for eg - your centre speaker has a response upto 60hz, and is set to small you need to set the AVR crossover at 60+Hz, preferably 70hz or 80hz. this will send all sounds below this frequency from the small speakers to the sub. any speakers set as large will not be affected.
as for your sub, since it handles the LFE channel apart from the redirected bass, and the LFE channel has lot of information even above 100hz, you should bypass the sub crossover (in your case it may mean setting the crossover to out) or set it as high as possible if it is not bypassable.
cheers