Calculating Use of Urinals

We are completing documentation on a LEED-NC project and are trying to come up with a sound methodology for calculating use of the building's lavatories. Specifically, Floors 1 and 2 of the building contain half-level work spaces with unisex bathrooms. The main floors, down or up just 4 steps, have mens and women's bathrooms, with the men's bathrooms having waterless urinals. We have "polled" various folks and based on this are making the assumption that approximately one-half of the male employees on the half levels will use the men's only bathrooms on the main level. While we don't have any hard evidence for this, everyone thinks it is a reasonable assumption to include in the fixture group calculations. We are even talking with the owner about developing a policy and signage encouraging male employees to do so to help conserve water. Is this a reasonable approach/assumption to include in the calculations for WE P1? DW