Taller is relative to where you more skittish fish are going to be. For example. Pentazona will be rather shy until they get comfortable and hang out low to mid-level. If you have plants for them to relax in they'll gain confidence (assuming you have at least 5) and come out in the open regularly.
My Angels and Cherry Barbs hang out midlevel so they'd want taller plants than what you have.
Perhaps in the corners you have a small copse of taller plants so as to not upset the symmetry of your aqua-scaping composition.