Vent now blows on thermostat
Yes, play with closing the flaps of however many it takes. It really depends on who, how &amp; when the ducts were installed, balance is the aim but the only thing that does get balanced (maybe) is what's in use at the time the system goes active.

In my house, I have to keep 2 vents closed year round &amp; then heating &amp; cooling seasons have to have additional &amp; different vents opened or closed for fairly uniform temperatures.

If things level out for you with just the thermostat vent shut, then leave it that way or you can possibly go to a new vent whose fins blow the air to either side &amp; never at the thermostat. Also, you might be able to move the thermostat out of the hallway altogether.