Takeoff problem after hand-launch in Mission Mode

I have a question about takeoff with PX4.

We’re using the Mission Mode for Takeoff. We’re wondering, distance between power-on and launch point is important or not. Because, when we launch a little bit far from power-on point, it can not takeoff proper. We guess UAV try to enter the route before lift off to secure altitude. So it can’t reach the stall speed. Then when it try to enter the route after handlaunched, it’s falling down. Is this approach correct?
Do you have any idea about that?