Fixed effect duration when clip length changes

Not sure if this is a Motion 5 or FCPX question: I am creating an FCPX Title in Motion 5 and have added the Sequence Text behavior to it. The title is set to say 8 seconds and the sequence text is set to 2 seconds. Using this text in FCPX works fine, until I decrease the duration of the text in FCPX. The change in duration will unfortunately also impact the duration of the "sequence text" effect. Is there a way to prevent that ? So is it possible to fix the duration of the "sequence text" effect to 2 seconds, even if the duration of the text clip is changed in FCPX ?

set a Marker at the end of the 2sec (shift-M)
right-click Marker, select Edit
change Type to Built-In Mandatory