Hello kjdunbar27, scheffleras are tropical plants, but they do have good drought tolerance. Drought tolerance though does not mean depriving them of water, they are not desert succulents. What you need to provide is well draining media, using good potting soil and adding more pumice or perlite to make it airy, not compacting too much in the long run. Then water thoroughly the root zone as needed, not making them sit in too much water.
I would suggest you position your plant closer to the window to get more natural light. Do away with misting of the leaves, there is not much air movement around there, so you are just risking fungal issues. Unless you can run a ceiling fan or open up a window a bit to allow more air around then that would be a good option.
If your weather permits it, you can bring out the plant and do a good power wash of the leaves, to remove whatever is there. It will love morning full sun, and dappled afternoon sun. I grow mine outdoors, and we get into a very dry and very hot condition here with very low humidity in summer to fall, so that is the time I really try to help them with some frequent misting and thorough watering at root zone. Definitely a different growing condition than yours. Just relating it to you so you will understand how drought tolerant it can go.
I have seen them grow as well in my homeland where they are left in full sun, but the difference is their temperatures are stable, not going lower than 70F everyday with occasional showers and rain, even typhoons, with high humidity levels. Our media there is loam soil with volcanic attributes so it s quite rich and well draining. Just letting you know again what factors will help this plant thrive better.
It is a balancing act for this part, not too wet and too bone dry. So got to adjust your watering regimen and plant positioning as the seasons change.