Those are rheostats (dimmer switch), not tstat. Basically it doesnt control the temp at all. You adjust the amount of power going to the heat mat with the dimmer dial. Its the same as a dimmer light switch. So if your temps get too hot or too cold it doesn't automatically adjust for them. That's what a tstat does. A tstat will either turn the heat source on or off depending on temp or automatically adjust the power output to keep it at the proper temp (depending on if its an on/off tstat or proportional).
You should look into getting helix, herpstat, or VE tstats. Even a hydrofarm would be better for now. A good tstat is gonna be your best friend.
If you put the probes on the outside of the tank, u adjust temps until they are what you want on the inside of the tank. So if you want 92 on the hot side, you may have to set the tstat to 95 to a achieve it. Make sense? You just have to be diligent about checking temps.