I'm on the coast of Lake Erie where winters are cold and indoor relative humidity is in the 25 percent range. I've had an Epson 7900 for 5.25 years. It resides in a basement, and so is relatively cool. I'm away several times each year for between two and 5 weeks, during which the printer is never turned on. In the early days a nozzle check would always show numerous missing nozzles when I returned. In addition I'd always have more clogging in the warmer and more humid days of mid-summer than in the cold and dry winter. This seasonal variation in clogging still happens, but to a far lesser extent over perhaps the last 2.5 years or so. Now it is common to find no missing nozzles on a nozzle check after the printer sits unused for several weeks, especially in winter and occasionally but not often in summer. Most recently this happened in late January through early February, which was some of our coldest weather on record, and therefore the driest indoors. I don't understand why, but the cooler the room is, regardless of humidity, the fewer clogging issues I have. In winter the RH is around 25%, but the room temperature can be as low as 63ºF unless I'm in there with the heat turned up to around 69-70ºF. The hottest the room ever gets in summer is 72ºF. In summer the humidity is limited to 55% with a dehumidifier.
Two things seem to happen. First, after a couple years of use the clogging decreased noticeably overall. Second is the very noticeable temperature vs. clogging relationship, which has always existed. Make of this what you will. I'm just adding it as a data point and YMMV. Humidity probably matters, but at least in my case it seems to matter a lot less than temperature.