I usually go with a 3 part army with steppe factions, 1/2 the horses go around each side and 1/2 the horses stay up front. I think a cresent is asking too much though TW controls don't lend to any geometrically complex formations.

More importantly, HA only armies are pretty useless after missiles are out. Its better to bring foot archers and infantry since levy HA will rout on charges.