As far as i understood, in case of regular home router, you should have these 3 rules in beginning of firewall filter forward, to use Fasttrack.
/ip firewall filter
add chain=forward action=fasttrack-connection connection-state=established,related
add chain=forward action=accept connection-state=established,related
add chain=forward action=drop connection-state=invalid
Note, that all packets that goes fasttrack, will not be visible in firewall and you will not be able to limit them in queue global.