Interesting. Both of mine are on continuously. And both park the heads in sealed cups. Proper head parking is known to make a big difference. Must be why printers that do not cap the heads combine the print head into the ink cartridge.
So, how old are your Epsons ? None of the ones that I owned ever parked properly. I wonder if they stopped doing it on later or cheaper models, for some reason. OTOH, my HPs have all parked to a sealed area, yet some of them have had the heads on the cartridge, and some haven't. The 5180 that I currently use, has external heads, but they have never clogged as long as I have owned it, so yes, correct parking is definitely significant in this.
Arfa