Every Echoplex I've heard over the years (and that's a lot of units) has sounded a little different from the others. I'm not just talking about tape aging, either.
I think the best thing to do is to play around and see what you like. Watch some videos if you don't have a unit to play with.
Start "authentically" by using just one voice/line (head) by setting LEVEL2 and FEEDBACK 2 to 0.
I've heard dark ones (high cut around 1K)
...and thin ones (low cut around 200 Hz).
MANY are "thin".
After you adjust EQ, also adjust feedback and mix until the balance feels right.
Then Isolate one area of the algorithm at a time and find out what it does.
One thing I've found is that most units don't have nearly as much of modulation as the typical emulation might suggest. If anything, it is often barely perceptible. The factory settings for MONO TAPE reflect this very accurately. You can explore different modulation settings as well. Set LFO DEPTH range to HIGH and set mix high while you work. Remember that LFO Phase controls do nothing while the MONO TAPE mode is engaged.
For "Flutter" (I like about 16 Hz). For wow I like it faster than most... almost memory-man territory (4-5 Hz).
Also, I like ducking, which feels a bit like compression. A tip for ducking is to set Mix to 100% while you dial it in.
Mix can be deceiving. Once you dial in your desired delay flavor, the "usual" settings may need revisitation. In playing with the MONO TAPE while writing this, I ended up with MIX at 80% and it sounded fairly balanced. EQ settings and ducking are in play.
Push feedback hard and see how the DRIVE control works.
You might simulate the Echoplex preamp with a (tape) DRIVE before or after the DELAY.
In some of my presets, I've used a synth block and filter to simulate the signature noise of the pedal.
Play around. The palette is there for you to imitate what you hear. One great way to learn to do that is to experiment.