I'm not sure how tall that particular Crypt gets, but if you wanted to add a tall background plant you could look into getting one of the types of Vallisneria (Jungle Val, Corkscrew Val).
It's an easy, low-to-medium light plant that grows nice tall strands that can be used both as a background or to create a type of "curtain" effect. They also wave quite nicely if they're in any kind of current which can add very peaceful movement effect to the tank.
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