Tirz certainly has a higher impact to the GLP1 receptors. Not as much as Semaglutide but certainly far more than Reta which, of the three agonists, the GLP1 is the weakest of the bunch. Hard to say how much, since everyone is different.
I'll assign an arbitrary # to it though to give you an idea but the hunger suppression of Tirz is at least 50% greater than that of Reta whereas Sema may be 100% greater than Reta & 50% more than Tirz.
Again, all arbitrary #'s but just to assign some sort of metric for conversations sake.
I've seen some people add in a little Tirz once per week at a start very low dose (if you got this route) strictly for the satiety effect. There was also some well-known "oops" scenarios where they were combined at the lab that were found in 3rd part testing (subtle reminder to test your peptides). I still think that this may have been more of a requested stack that got mislabeled or something along those lines more so than I think it was a legitimate mix-up by the labs.
Using a little Tirz w/Reta as the primary weight loss peptide may result in a lower Glucagon agonist (since you likely wouldn't be dosing Reta as high to titrate for weight loss if you're getting those other two agonist as overlap from Tirz also) so while it's common, I'm not sure it's the best way to go. Maybe for some though.
You can also check into Cagrilintide as well. This may be a better option if all you want is the satiety effects since Tirz will not only be adding a stronger GLP1 agonist to Reta but it will also increase the GIP agonist as well. Common dosage for this use is 1.5mg sub-Q once per week. I'd suggest starting with 500mcg though to see if that gets the desired effect.
Keep in mind that the half life of Cagri is about a week so it takes about a month of weekly injections to reach a steady-state in your system. It's best to give it a month to reach this level to see if it has the desired effect on hunger. If not, move up to 1mg and finally 1.5mg per week, if needed. You can go up from there but I'd take smaller steps and give the increased dose time to reach a steady state each time.