I'm growing it as a Semi-emersed/Aquatic (it is early and I'm sick so I can not recall the term) I would say 1/4 of the plant is under the water with the rest growing above the water line. All the medium is above the waterline by 1/4'-1/2" unless I get behind in my watering like I am right now. So it is likely more emersed than I prefer.
I'm using the pond mud I picked up in Japan so many years ago and since I can not read Japanese I have no idea what it is, just that the UG loves it. It has never rooted into the mud but does manage to get a good hold onto the first 1/32" of the medium, when I remove a section it DOES NOT want to come out. But there is never any real mud to talk about remaining, a quick 10-30s wash in the sink and the mud is all gone.
IMO if you are trying to keep the plant happy, flowing clean water is a must. Think of a slow moving sandy river with some fallen branched for the UG to attach to.
My 2nd go would simply be a nice piece of Aquatic quality driftwood, figure out how high on the diftwood you want the UG to grow up it and then play around with the water level until the wicking effect of the diftwood fits your desired height, again flowing water seems to help a ton. Any sculpted aquatic growth with UG would take alot more effort, a small take would not be bad but a 90G would be a full time job.
If you want to know how to flower this plant ask someone else
I've seen 2 flowers and missed about 3-7 more over all these years and I've mailed out enough to have EASILY carpeted my entire 2000+ sq ft house......no I'm not kidding, I'm not trying to grow to sell it anymore and have 2 more sqft ready and waiting on me to well feel up to mailing it off.