"..but looks like an unnecessary risk when the prey is twice as long and tall as the predator." --DM
What is risky about reaching up and grabbing a sauropod by the neck, if you match the physical description of a tyrannosaur? If your hold is 2m behind the head, you are 8m away from the front feet. Even that assumes no injury to the spine of the prey item, which would result in instant incapacitation of the prey.
It 'looks like' to me like you are characterizing prey/predator interactions on the basis of sheer intuition, and are overly impressed by simple size differential.