Are you spray starching? I don't spray starch any more because (1) I don't like the overspray, and (2) it's hard on my hands if it's pump-type and hard on my index finger if it's air-propelled. If I were to spray starch, I would definitely use a large flat sheet to catch overspray.
My preferred method of starching yardage is to use a mixture of Sta-Flo liquid laundry starch and water. I use my kitchen island, which is a good height for this type of work and cleans up easily with water. To apply the starch mixture, I use a large wall painting brush. The starch goes on quickly this way. I just unfold the yardage as I apply and try to make sure I get all surfaces. Afterwards I allow a couple of minutes for all of the fabric fibers to absorb the starch, then toss the yardage in the dryer and iron with steam. This is the fastest and easiest method I have found for starching yardage. A side benefit is that I never get burned starch on my hot iron this way (which can happen with spray starch that is just sitting on top of fabric and has not been absorbed).