It is a strange lookng formation. If there were a mile of ice and the asteroid went through that before hitting dry land what would the result look like and what about when the glacier eventually melted and left along with the regolith? It might look like that.
The top of the lip is kind of flat. This might have been the level of the ice and stuff above that would have been blown all over the landscape. Also, the impact need not have been vertical: note one side is lifted: the remaining mass of the impactor would be under that side.