I assume we are talking about a static wind or seismic load. I assume the differences are fairly small. If so, then this is because the loads are applied to the diaphragm area for seismic loads, or the edges for wind loads, and since the beams as well as the diaphragm are elastic you will experience non equal deformations along the length of the frame.
Answer Verified By: Minsun Ku
Thank you for prompt reply.