My own experience tells me anything over 20% leak down is probably (not always) a mechanical malady. I did powertrain at a dealership for the last few years, we were generally never wrong when it came to those numbers, almost always a cooked valve, broken valve spring or a seat that dropped out. These are mostly hydraulic cams we're dealing with so apples to oranges but I'm just not sure that such a significant amount of leak down can be adjusted out.
When I think of a lash adjustment with mechanical lifters, it's generally a few thousandths of an inch. Taking that into consideration, I'm skeptical that over 1/3 of the cylinder fill volume is leaking because of poor valve adjustment. Prove me wrong, I'd genuinely be interested in seeing it. Even then, if the lash has backed off that much, I would suspect worn or broken parts. Just my 2 cents, take it as you wish.