I keep getting a lot of these Entomobrya that look like this, on redwood posts, usually using the moss for cover. They have a very distinctive back, though look at all of the listings for these in bugguide, the closest I can find is Entomobrya multifasciata, and the markings just aren't quite right.

What do I need to have a photo of to be able to ID this one?

These are the only Entomobrya I'm finding on the redwood posts, the other 2 I've seen on occasion are on metal or someplace not colonized by moss.

could be an alternative tentative ID, given you found many of them.
Drepanura is closely related to Entomobrya. The difference is easily seen in the shape of the mucro (using a microscope...).
In Drepanura the mucro is falcate (one terminal tooth), in Entomobrya it is bidentate (2 teeth).
But in habutus, both genera look alike...
To confirm this tentative ID we need more shots of the dorsal pattern. This pattern is quite variable. So we need shots of several specimens to be sure.

Here is a different day I submitted this same (apparently) Entomobrya

I'll add more anterior shots to this folder, as I'd avoided them thinking they had no ID value.

Thanks to your recent upload I found out that I have systematically misidentified such specimens as Salina mulcahyae...
Time for a cleanup ;-)
Your current upload is of juvenile Drepanura californica, given the relative short antennae.

I've noted different sized ones over a period of time, from 1-2mm that looked alike. I though I had more good photos, probably did, Windows just dumped many folders of insects I had made into a file system, as when duplicating the folders, if the name was too long, it deleted my originals, as well as not making a copy.