Rashi (Ex. 28:6ff) uses the verb "choger" in reference to how the ephod is worn, i.e. "wrapped" behind the Kohen's back, rather than in reference to how it is tied. Two verses later, Rashi refers to the cheshev ha-ephod as a "chagor" or "chagorah", i.e. a belt, by means of which the ephod is tied around the Kohen's body; here he doesn't say that the belt was tied in the back. There are two pictures of the ephod in the article "Ephod" in the Talmudic Encyclopedia, and they both show the belt as tied in front. The ephod itself was worn in the back, according to Rashi; Rashbam has it extending all the way around the body so its sides meet at the front.
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