Welcome to the forum.
Your briskets were cut from the flat. You don't mention the USDA grade...they could have been Select or Choice. My initial suggestion would be to find a small USDA Choice packer iso flat. Packers include the "point", which has substancially more fat.
In general, flats tend to yield less moisture in the finished product. One trick used by many brisket cooks, is to wrap the brisket tightly with foil when it hits the stall/plateau stage of 170. The theory is, foiling helps prevent moisture loss. There's a lot of argument on this but I'm an advocate of foiling flats; not packers. If you choose to wrap with foil, foil tightly. Air pockets will accentuate steam and moisture loss.
As to you injection question...hard to reply without knowing what you used to inject with. Most commercially sold brisket injections contain phosphate, which helps retain internal moisture.
Next time around, buy a small (10-12#) packer, inject it and set the Smokette for 250. Inject from the bottom (no fat side) and smoke it fat side down. I think you'll be a lot happier with the results.