It is known that Amestris is using the West's heavily populated army to tire out and weaken Creta's forces. Creta is forced to use heavy amounts of men while Amestris has to use only the Western branch of its military to fight, meaning that if Amestris focused all of its might on Creta it would most likely overwhelm the foreign nation. Amestris has been using the Western town of Pendleton as a morale booster for its army because it's the first town Amestris won in the border war.
Due to Bradley and the Homunculi, much blood has been shed on both sides. Though Creta and Amestris are both using approximately equal amounts of men, Creta is forced to use a much larger percentage of its total forces.