Another thought. Would it pass muster to carry a fixed blade in a pocket like this, with the grip exposed? …
I hate to sound overly cautious, but I would advise against carrying a fixed-blade like that in California. 99 out of 100 LEO's might not have a problem with it, but the fact that most of the knife is concealed from view could very easily give that ONE LEO all the justification they need to claim the knife was concealed. And if your shirt came down over it, that would be even worse.
I carried fixed-blades in San Diego for many years (one at a time). For about a year or so I carried a small fixed-blade in a back pocket sheath with only the handle visible. A few different LEO's saw it and didn't have any problem with it. But my attorney warned me against carrying it in such a way. He advised me to carry any fixed-blade so that it was fully visible from the tip of the handle to the bottom of the sheath so there was no chance of an LEO claiming it was concealed. I decided to take his advice and started carrying my fixed-blades "in a sheath that is worn openly suspended from the waist of the wearer", which is exactly how the law defines a legally carried fixed-blade (CA pc 20200).
As far as what constitutes a "concealed" fixed-blade in California, there are no laws or case laws on how much of the knife must be visible to be legal, but there are case laws that refer to the "intent" of the person with the knife being a major factor. If there is reason to believe that it was the intent of the person to try and disguise the knife or hide the knife from view, that goes very badly for the defendant. Unfortunately this is a very subjective standard, so it can be very easy to get screwed in court.
On the bright side, there is case law that protects people from prosecution for things like carrying an object that temporarily blocks an openly carried fixed-blade from view, as well as exclusions for, say, an LEO not seeing the knife because he's looking at you from your right side, and you're wearing the knife on your left side.
My general advice when it comes to knives and California is to err on the side of caution. Although California has become a very weird place in the past few years, with prosecutors in some counties refusing to prosecute people, and as a result LEO's being less inclined to arrest people for minor offenses, there are still places where prosecutors take a hard line and will happily pursue a weapons conviction.
I make a concentrated effort to follow the letter of the law down to the finest detail when it comes to knife carry. Like I said, 99 out of 100 LEO's might not care one bit about an ordinary persons knife, even if it's an illegal knife, or a knife being carried illegally, but if you're unlucky enough to run afoul of that ONE who wants to make an issue out of it, and you live in a part of California where they still like to prosecute people, making the wrong choice about the knife you carry, or how you carry it, could turn your life upside down and inside out, and speaking as someone who has been through the system, in my opinion it's just not worth it.
So maybe I am overly cautious

. But jail can be very unpleasant, lawyers, fines, and court fees are expensive, a criminal conviction can mess up your life, and probation really sucks.