In the 757, the least EPR I've seen during an idle descent is 0.97. The engines are RR RB211-535E4s. Seems to me like they probably have some sort of ram-effect compensation since I've never seen what you described in the L1011. If that's the case though, it would appear that pressure in front of the fan is higher than at the end. I don't see why it isn't possible.