Hygrophila lancea flowers easily too and is a very hardy WK plant. Roy (greenfinger2) sended me a few cuttings from this plant last year and they where already flowering. Grew them on an now are flowering again. He sended me another one with a flower but i forgot it's name, something with Rubra.. I bet you'll find it back with flower if you search his wabi kusa journals.. Pogostemon is also a very good plant to grow emersed it takes lower humidity very good but i yet not managed to make it flower, but it can i've seen it. Most Rotalas also grow very good emersed and a lot of them flower easily. Also Heteranthera zosterifolia i've seen growing emersed and flower.
To make a plant flower is not always easy depends on the species and geographical origine some need specific light hours and or intensity others need some specific soil propperties to induce flowering like a potasium or phosphate rich substrate.. Some plants just do not flower indoors at all which probably is a light intensity issue, i do not realy know why. I think sometimes even temperaturs play a role, like we had a very chilly presummer this year and i have much less flowers this year then last year.
Anyway if you have a plant of which emersed and outdoor cultivation data is available then usualy they also give a flowering periode, like from this month to that month. Try to mimic the lighthours from that periode. For annual plants the shorter day hours induce it to flowering because it wants to propagate by seeds before it dies. With perennials it can be from early summer to late summer or all year long. In our trade where the data is aimed towards aquatic cultivation and propagated by cuttings this flowering data does not apply. This way we can rejuvenate and grow on an anual plant for multiple years.
Some time ago i found a scientific paper where was stated that not only light hours induce flowering and there is much more to it. Unfortunately the article was not in depth.
I'm only an intrested hobbyist flower freak and do a lot of guessing in this part.. You might ask
@dw1305 about this subject, he's a botanist..