I have a network running with a Dec x55 as router and 2 satellites hard-wired to another floor and a detached building. 

But I have gotten access to a Fortigate device and would like to switch over to using that as my router and security device, so I want to switch the deco over to AP mode but keep the Deco network in place for wireless (and remote wired via the satellite LAN ports) endpoints. My main question is, does AP mode have the same "roaming" advantages as router mode? As in, if I'm carrying a wireless device that's connected to one radio through my house to somewhere that it would lose signal with that radio, will it seamlessly hand off to a satellite that's closer with a stronger signal?  Because right now, that works perfectly, never have any issues, don't want to lose that.