Ahhhh - right!
I would definitely write up a extension to handle this instead (if you have the pro version of SFS).
Depending on the type of game you are doing it might even be required to have the server being the authority running the simulation and cheat checks.
E.g. you code up a "SendUserPos" extension method. Each client sends those to the server using raw or even additionally compressed by you in the client/server code.
Server can then run checks if that position is truly valid (e.g. did the player suddenly exceed the maximum movement speed = most likely cheating) etc.etc.
Server can then update its internal position array of all players, and even selectively send out position updates.
For example, if 2 players are far away from each other they might not need to know where they are. So you dont have to send out positions of each of those to each other. Another player might be right next to the first player, and thus needs constant updates. Players "almost out of sight" can get every 5th update or so.
A lot of similar mechanisms can be implemented server side.
And if you are truly concerned about cheating and making e.g. a FPS, then you have to send from each client what they pressed (e.g. move forward), and have the server tell the client if its OK to move forward and at what speed and position you have. Requiring you to implement prediction and interpolation on each client
Its a minefield with tons of opportunities
But for many games where you are not concerned about cheating as much, you can simply use the server extension to throttle bandwidth usage by e.g. zoning and similar.