Your math is correct. All sensors + Thermostat\total # sensors +1. However, this may not be 100% accurate. See below about Sensor Hot/Cold spot settings and sensors “dropping out” of Comfort Control.
In my experience with mine, if you are looking to get the same temp in all rooms, the Thermostat with the Remote sensors will NOT do that. That goal is a dead end. The Thermostat / Sensor combo cannot fix Air Delivery variances.
With a single, conventional non-variable HVAC system, the Thermostat and Sensor control system has no way whatsoever to deliver more heat or cool air to any single room without also delivering the same to every other room in the house. The air delivery ducts and registers control air volume to each individual room. The temperature of that delivered air is highly affected by the physical topology of that duct system and how it was calculated, engineered, and installed. The Thermostat and Remote Sensors cannot overcome construction limitations.
During heating for example, when one room is cold, it brings the average down, calls for heat from the calculated average, and heats all rooms, not just that room. It will bring the heat up in all rooms to raise the average until the thermostat is satisfied and turns the heat off. However, if your duct work and registers are delivering more air to one of the warmer rooms, that sensor will rise more than the cold room, thereby offsetting any heat gain in the cold room. The Thermostat will end at an average temp wherein the cold room is still not up to the desired temp and the hot room will be well over the desired temp. If it does successfully eliminate the cold spot room, it creates a hot spot room in the process.
The only way to get an equal temp in all rooms is by installing a variable zone Smart HVAC unit capable of delivering more or less air to each individual room based on need, installing smart registers capable of restricting air delivered to specific rooms based on need, or run around the house each season change adjusting the registers to balance air delivery.
My old house has a retrofit unit at one end of the house with registers that have been cut into several rooms while other rooms use original construction registers, some with original ducting. The system was installed by the previous owner and the company hired to install was the lowest bidder. The installer was obviously clueless about air delivery dynamics over distance. They used the same size flexiduct on all new registers regardless of the distance and it is wildly undersized compared to the original duct used. To make it even more inefficient, the longer runs are tied into the main trunk duct further from the unit than the shorter runs. The result: rooms closer to the unit that are connected to the main delivery duct closer to the unit with original, larger ducts get nearly twice the air delivery of rooms farthest from the unit. I have to manage room-to-room temp manually by adjusting registers to restrict airflow.
I set my Fan Activation Delay to “By Furnace”. But, I have a NG Furnace which operates on a completely different pre-heat principle before the fan activates and a cool down pre-set before shutting off. For Cooling, I also use the Coast To Cool setting that maintains the fan at a higher speed after shutting off to get every ounce of cooling out if the coil. I have my Fan Cycle set to 0m/hr. How these settings are managed and if they are even available to set depends on the type of HVAC system employed.
There have been many discussions since the Sensors were released about what causes them to spontaneously drop from being included in the average for the Comfort Control group. Some have mentioned that if a sensor falls outside of its preset Temperature Threshold, that it is excluded from the average. I have been successful in locking mine into included status permanently. I tested this by dropping the temp on a Remote Sensor drastically beyond the Temp Threshold and could not get it to drop out of Comfort Control. I also have my Motion Sensing turned off.
The Thermostat Firmware also “appears” to have some logic in it to somehow weight each remote sensor individually, though no one yet has specifically identified what that logic is or how it changes the calculation. Each sensor has its own Hot/Cold Spot setting for Prioritize Savings, Balanced, and Prioritize Comfort. In theory, this setting would place a weighting per sensor to raise the priority when set to Comfort and lower the priority when set to Savings. But, no one has yet identified what that weighting or priority math is or if it really exists. I would assume then that the Thermostat, with a similar behavior setting, is also prioritized when working in concert with the Comfort Control Group, but I have no way to confirm this.