To keep mine submersed, I trim off any leaves that exceed 3/5 of my tank height. I find it more effective if I trim a few leaves at a time. It reduces shading and the next few leaves stay short. I guess it forces the plant to put out more leaves in a hurry too, and not expend energy pushing leaves towards the surface.
I suggest you trim off majority of your emerse leaves. Leave a few for photosynthesis. The new leaves should pretty much stay short. If not, once the new leaves open up and are able to contribute to photosynthesis, trim off the remaining emersed leaves.
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