You have me wondering if I placed the probe into the larger casing and let it go to 153 just how much higher will the IT be on the smaller sausage and will it hurt anything ? Just have to experiment to find out I guess ? I am already half way through the smoke so I will pull the rings out and finish the larger casing .
I do exactly this.
I put it in the bigger sausage or the sausage in the coldest spot of the smoker.
I run multiple probes so I also probe in the hottest spot of the smoker.
I pull my sausage when the lowest reaches like 152-153F.
Often the highest sausage is like 158F but it hurts nothing even if it is slightly more cooked.
The overall product is fantastic and there are only a few that might be a little crisper than the others. To me, this is so simple and easy, that a slightly more cooked sausage or 2 (which still taste amazing) is not worth all the hassle of loading/unloading in multiple goes, etc.
Simplicity is often the best approach and what you are thinking about is what I do and is simple and good :D