The ft group will be configured in the admin context and e.g. looks like this.
ACE 01:
ft group 1
peer 1
priority 140
peer priority 100
associate-context FOO
inservice
Within the context FOO you configure the HSRP TRACK.
ft track hrsp HSRP-Track-FOO
track-hsrp
peer track-hsrp
priority 50
peer priority 45
In an event of failure for the tracked group on the active member the priority will be decreased by the amount specified in the track group. So the active priority will be below the standby priority and therefore trigger a switchover.
That is at least what the documentation says. The other way around it will probably increase the priority by the amount of the peer prio.
Have a look at the link it probably explains it better. :)
http://www.cisco.com/en/US/products/hw/modules/ps2706/products_configuration_guide_chapter09186a0080683a15.html#wp1036073
Hope it helps...
Roble