From the wikipedia page on the Chicxulub crater
Along the edge of the crater are clusters of cenotes or sinkholes, which suggest that there was a water basin inside the feature during the Neogene period, after the impact. The groundwater of such a basin would have dissolved the limestone and created the caves and cenotes beneath the surface.
Considering that the impact site is going to be messed up quite a bit by the impact itself, more than the shape of the impactor I think it is important to have the right composition of the ground: caves, cenotes included, form because water dissolves limestone. Considering that limestone deposits after the impact (whatever is there before will be morphed by the impact heat and pressure).
For the shape of the impactor, considering that the Earth crust ranges in thickness between 5-10 km for oceanic crust to 30-50 km for continental crust, I don't see that big difference, because once the crust is removed and the mantle exposed the consequences are pretty much the same (Chicxulub crater reached 30 km of depth).