Different air flow could make a plant dry out faster. Did you ever keep other plants in that location? How did they fare?

FataMorgana

Yes, other plants have grown there. And thank you for asking this question. The light, in concert with the air vent and the three foot height difference, may make the difference.

The plants that tolerated the wire rack window were the geranium, the violets, the vegetable seedlings, and the sedum. "Tolerated" because they didn't have enough sun.

The plants that didn't like the wire rack were the phalaenopsis orchids... too much sun.

The phalaenopsis orchids are over on the floor in the traffic area of the patio door... happily blooming out of season about 1 1/2 to 2 feet back from the door. The rau ram was happy in their vicinity. Sigh. I guess the rau ram stayed more evenly moist and got more indirect light in that window than I realized.

The ginger plants and lemon grass are going to have to come in soon. I wonder which window they'll tolerate most easily!

I have always thought of this room as the windy room, because the air moves so. But for some reason there is no breeze in the traffic area by the patio door. That could definitely have made a microclimate that is more humid and less drying around the patio door plants.

Most likely the soil is drying up due to the air flow. Rau Ram thrives when grown in a wet and humid environment. Try covering it up with a clear bag. Make sure to put some small holes for air. It is like your very own little green house.

Good Luck,
Duy