You can place a round by selecting intent edges or intent surfaces. Using intent edges or surfaces makes selecting references quicker. They are also more robust, preventing rounds from failing when model changes are made, since the references for the rounds are tied to the features in the design model, not the individual edge references. In the upper figure, the round is being created by specifying the intent edges. In the lower figure, the post feature is moved to the right, over a bump and into a gap. Though the resulting round geometry differs, the round is still successful. Even when the post is updated from five sides to four, the round is still successful.
The following are examples of intent edges for a rectangular extrude coming from a block:
So, for these examples, the shape of the rectangle is not important – only that an extruded feature is present.