I'm betting it's not small and is much more significant in the areas of the universe that are extremely vast, mostly empty pockets of almost nothing, or empty space, etc, and yes, I think it is primarily those areas that are driving most of the expansion among/around/through all the other, much more normal gravititationally bound/attracted to one another, clusters, superclusters, and strings, or much more regular matter/energy/material, of clusters, superclusters, and strings, of much more normal galaxies, etc. And I even think these areas even play a very significant part in them even being able to be arranged that way, etc. The other part is the rest of those clusters/superclusters/strings/galaxies much more normal gravitational pull on or towards one another, etc.
Anyway, I have to go for a while, I'll try to get back to you more later.
Later/Take Care.