In the majority of cases, you will want to set your speakers to "small" so that Bass Management can be enabled for that speaker. Large and Small can be misleading settings since most tower speakers would reasonably be considered as "Large" by most people. In fact: "Small" = Bass Management enabled. "Large" = Bass Management disabled.
Home Theater systems are designed to take advantage of the blended bass made possible with Bass Management. For a very detailed write up on how to configure this properly, take a look here: https://martinlogan.com/en/subwoofer-setup