B737 Captain reported a loss of control on ramp when plane rolled back into a ramp depression at the gate. While attempting to pull further forward Captain noticed a ramp person with chocks under his window prior to it being safe to approach the aircraft.

Narrative

Reassigned to gate XX in a B737-900. Per ramp tower; given direct entrance. Wing walkers blocked the service road as I made a hard left turn; then dog leg or oversteer to a hard right turn (guidance on my own); then a very short forward to the guide person. Coming into this gate before; knowing it slopes up and there is a divot or transition from asphalt to cement where the nose tire stopping point is. I did have 2 engines running and about 40% N1 on the #1 engine. It was a slow marshaling in straight forward as we were very heavy and hot outside taxing on the asphalt segment. Poor marshaling technique as he brought the tips of the wands together to the (X) position. We shut down number2 engine; but then the guide person reopened the wands and told me to come forward. Before I brought back number 1 throttle I let up on the brakes; I noticed a person with chocks walk under my window (before being given the OK to approach the aircraft signal); the aircraft rolled Backwards into the divot and the guide person stop with the wands and screamed at the chock person. I saw this person lunge out from under my window straight towards the running engine. Eventually; we moved the aircraft to the correct stopping point and secured the aircraft. I did talk to the gate supervisor of the issue.