NavmeshAgent path problem

Hi guys.
I've a problem with mu units' NavMeshAgent .
Originally, my units have destination where blue "X" is in attached image and they are walking along blue path.
They are walking on ramp (they are along the red arrow end) when tower shoots my units (red line) they are allerted that someone is attacking them and they change destination with tower position (violet "X").
The problem is that they completely change and they come back to follow violet arrow.
Do you know why and how I can change their destination without completly change path?
Thank you very much.