Yep, Central Florida is a region.
South Florida with the ficus trees 40 ft tall beside the highway starts at about Pt St Lucie and I'll go ahead and call it the city of S. FL. It is one big metropolis.
Glad I had that 16 valve V8 so I didn't get run over! Loved driving over that elevated section somewhere near Miami that's like 40 feet above the ground, That's better than a long bridge that you can't see land in either direction
My opinion is your experience is very similar to mine. I could have tried harder to get my speaker and seat position correct so I don't know if it might have been possible but I just didn't work at it hard enough. Correct placement for the gentle slope network might not be the same for the ES.
Also, don't forget to look for other causes... look around the room... did furniture get added or moved around since you had the other networks?
They actually work better in a vertical orientation. See Toole's book for a discussion of the pitfalls of center loudspeaker designs--namely the horizontal orientation of drivers vs. horizontal off-axis frequency response.