FWIW, I have a few strains with incredibly small seeds: DJ Short's Blue Velvet and a landrace known as 'Nanda Devi'. On the other hand, my Uttarakhand seeds are monster sized. I suspect this has to do with the bract size genetics since it has proven to have nothing to do with the plant size. The Uttarakhand and Nanda Devi outdoors always end up 10-14ft tall, the DJS Blue Velvet stayed short both indoors and out.
When I grow or select seeds I have found that the color of the seed tells me more about viability than size. I like to let the seed covering almost fall off on its own before I know the seed is ready...nice and dark or spotted like a bird's egg.