SHT31 looks high and you wanted to compare with another instrument I can confirm it does run high.
My findings on the SHT31 are disappointing with humidity. After long term not happy at all.
Compared to my previous 11 and 15, the 31 is a rock star. I've used two 31's and they're virtually identical, between 1% and 99% this thing is absolute money. When I reach 1%, the dew does get a little cold, but a RAWS down the street does exactly the same thing. I also was W0X0F last winter and it wouldn't pull the 100% trigger, so I get that. I know you've seen some "competitors" PWS's, if you want disappointment, that's where to look. I don't know any sensor that's affordable that can mach the 31, not even close.
I typically don’t compare to other PWS systems except for RainWise units, Texas Instruments etc. I don’t compare it to cheap stations. My main stations for comparisons are ASOS, AWOS, and RAWS. RAWS stations typically read closer to the Davis stations than the ASOS does. There is one AWOS station around 30-40 miles east of me and their DPs reads very close to mine station or even the same at times.
I’m curious to know how the RainWise and Texas Instruments stations DP readings compare to the ASOS units.
The Earth Networks (used to be known as WeatherBug) stations DPs read closely to ASOS.
I’m just waiting from Weather Metrics and see what the specs are for their units.