You certainly can reduce your water, and that’s where I would begin. “Spongy” sounds like your moisture content is too high, whereas too much cure would come across more “rubbery.” I only add 8 oz (1 cup) of water to my 10-pound meatblock for Summer sausage, but I add the very same amount of Sure Gel, though (68g or 2.4 oz).
Also, stretch out your cooking time. I used the Meatgistics smoke schedule the first time I made Summer sausage, and I didn’t get the semi-dried texture I was looking for. It was good sausage, but it wasn’t that firmer, concentrated, semi-dried texture. I stretched out the cook for the next time, and I was much happier with the result. I need to look at my notes, but my schedule was something like:
110 - 1 hour (no smoke)
120 - 1.5 hours (no smoke)
130 - 1 hour (add a full bowl of sawdust)
140 - 1 hour
150 - 1 hour
160 - 1 hour
175 - until the internal temperature was around 150F
Finished in 160F sous vide until temperature was 160F
Cool in an ice water bath for about 10-15 minutes, and then leave out for casings to dry (like in the Meatgistics post)
I kept the times from when the cooker actually got to the target temperature, rather than from when I set to that temperature, so it was a much longer cook–about 12 hours. It’s a long day, but it’s totally worth it. I have considered cutting back on water to shorten the cook, but I’m concerned about how that will impact mixing and stuffing.