Yea seems whatever works best for individual. Mate of mine done awesome on sema stacked with tiny bit of cagri.
Reta is a triple receptor agonist so acts on GLP-1 receptor (same one as sema but not as much as sema does) but also acts on GIP and GCG for insulin and heart. Tirz is a double agonist with more action on GLP-1 than Reta but is GIP insulin receptor agonist also. So Sema is single, Tirz double and Reta triple. They used to nick name Reta triple G.
There are some good diagrams about showing which receptors which ones act on.
Iv finally got to goal weight so ready to taper down now. Need to update my profile pic. Still not super skinny but can’t get skinnier at my age without looking like I can cancer in face