The Research Excellence Framework (REF) follows a set of submission rules. Here we analyse whether the submission rules of the impact element arguably shaped the submission sizes of the submitting units -- a group of academics researching on a specific subject area in higher education providers -- to the REF in 2014. The number of impact case studies required was determined by the number of full-time equivalent (FTE) staff members submitted by the unit. We argue that units that did not have an extra impact case study or units' perception of lower quality of additional impact case study made some units to lower their submission sizes. We show that there were proportionately more submissions with a size just below the threshold FTE -- a threshold used to identify the numbers of impact case studies -- than those just above the threshold, suggesting that some units arguably decreased their size to return fewer impact studies.