I don't think the smallness matters as much as the number of seams you have to match. That's what makes it difficult. Of course, the smaller the pieces, the more seams you usually have to match and the less space you have for easing.
Someone on this forum posted about using Elmer's glue instead of pins on seam joins. I tried this the other day and found it works better than pins for me. It does require some time at the ironing board. What I did was place a pin straight down through both pieces into the ironing board cover, lifted the seam allowance next to the pin, put just a tiny dot of white glue in there, then ironed the seam allowance closed. It held really well, and my joins were as good as it gets with me.
I did find the glue migrated a little past the seam so, when ironing the pieces open, I first had to tug a bit to unglue the front. I have since gotten out one of those little glue bottles with the tiny tip and plan to use that for smaller glue dots. Also plan to place a piece of damp sponge in the bottom of a jar so I can leave the little glue bottle upside down when not in use and still have the tip stay clear.