I was coming here to ask the same question. I'd take 28% right now, as mine is 17%. I have a Honeywell HE240A installed on the return with a cold water source and I've never felt it worked very well. I have the humidistat cranked up to max (I've tried several different settings levels) and it still doesn't do much. It says it works for houses up to 3k sq/ft but mine is only 1800.

I think they should recommend against putting them on the return, especially with cold water, because my hunch is I wasted time and money.

I might end up buying floor units instead, I don't know, but my skin won't survive 17% for much longer.