Referring to the "sheet" that trims the pole aft as the aft guy, the benefit of an aft guy that is trimmed to the midsection of the boat is that it results in much less load on the
line due to a wider deflection angle on trim block, and it also doesn't have to bend around the shrouds. When the pole is trimmed somewhat aft it really doesn't matter where the aft guy turns, midsection or at the stern doesn't matter so much. But when the pole is forward, say almost to the forestay, the load on the aft guy goes up enormously - the load on an aft guy trimmed to the the max beam rail may be heavy, but should be adjustable. One trimmed to the stern may have so much load and friction (from the shrouds) that you simply cannot trim it...The load on the stern trimmed guy would be about three times as much as the load on a midships-located guy, just due the the higher (close to 180 degrees) angle of deflection of the stern located block.
You can have the benefit of working with only two sheets by using tweaker blocks on the sheets. Trim the tweaker block on the
line serving as the aft guy to change its trim location to the midships toerail. As you get much over 32 feet lazy sheets become the more common solution. See
spinnaker.php" target="_blank">http://www.harken.com/rigtips/
spinnaker.php for more specifics.