Confusion about parameter tstep_fraction of function create_grasp_approach_metric()

[linhy97]

Hi, when i see the Grasp Approach Vector Section, i am a little confused by the usage of tstep_fraction parameter. In the document, it states t_step_fraction specifies the timestep fraction to start activating this constraint.
Here are two questions i want to ask for guidance:
1） I wonder if the parameter tstep_fraction means that: after such percentage of path plan, it will start to consider the offset pose. Thus, the value range is limited to [0, 1]? And how to set an appropriate value. I find in my situation, sometimes it will appears MotionGenStatus.FINETUNE_TRAJOPT_FAIL.
2）Is there any parameters or function to set transition points in the plan process without pose constraints?
Hope for your help, thanks~