Helium should diffuse better out of pore spaces as a smaller...

Helium should diffuse better out of pore spaces as a smaller atom, yes. I also suppose that as a noble gas, it won't have the chemical bond attraction that molecules like methane have that causes them to adsorb in the reservoir, or miscibility issues that happen between oil and water, for example. But both diffusion and desorption are slow processes and I don't think they will be the deal maker or breaker. It would probably just mean that the composition of produced gas would be higher in helium than the in-situ reservoir gas composition.