You asked a question that has some different answers depending on what you assume.
What's that mean? To drop the Fs and keep everything else equal, the easiest way to is to add some mass to the cone. Then change other driver parameters as they falls out from the one change (compliance/etc); there is no such thing as two drivers with same everything except Fs.
Anyway, if we lower the Fs via added mass, it will have a little more output at tuning. Primarily this is a "normalized response" artifact, i.e. level matched. Really you have a touch MORE output right at tuning and LESS output up top as governed by increased mass.
Attached is a pic of an ultimax in 11cuft box tuned to 20hz, standard and a cone with about an extra pound of mass added to it.