Personally I'd push Reta higher first before layering in anything new. Got up to 20mg of Reta before adding .25mg of Sema.
Hit my first target weight this week, currently tapering the Reta amount back, missed one of my split doses and I'll take 6-7mg Monday instead (splitting doses is my usual approach). Haven't bumped Sema in a week, waiting to see if symptoms return, mainly that food chatter.
Went with Sema since I hadn't tried it yet, and it's given me the roughest side effects by far, though relatively speaking still fairly mild, mostly showing up whenever I tried increasing the amount... Originally planned starting at .5mg weekly but that turned out to be a mistake. That very first .25mg dose completely silenced my food noise. Ended up splitting .125mg twice weekly, occasionally bumping to .1875mg.
Basically, until side effects become the limiting factor, my general approach is to keep escalating to hold onto effectiveness.
I'd push Reta further, at minimum reaching 12mg weekly. Then add in a single milligram of Tirz on top, watch how the body responds, and adjust as needed.