You can definitely have very high concentrations of gas that...

You can definitely have very high concentrations of gas that refuses to budge, or vice versa. It’s to do with the permeability of the rock ie if the pores within the stone are poorly connected, then whatever gases you are hoping to produce are considered tight, (hence the need to frac unconventional tight natural gas resources, which are generally older formations ~250m years of age - what you’re doing is opening up the pores.) I’m generalising here based on natural gas, but really it’s the same for any gas down there. I found this from your Sep Independent Reservoir Rock Characterisation Study Results Ann that should provide optimism, (although I’m yet to be convinced they are claiming they found any significant hydrogen at target depth where the helium made a guest appearance):

• Porosity and permeability were found across offset wells, supporting the belief that the Ramsay area has capacity to flow hydrogen gas.
• Offset well chip samples and lab rock analysis also indicate that there is microfracture and a fracture network in both Cambrian limestone and fractured basement, supporting the Company’s theory for hydrogen gas migration potential.