Sounds like you are getting there, and it is confusing. The setting allows you to move your next focal plane closer or farther to/from the previous focal plane (plane of sharpest focus). IMO, all you can do is experiment or have a very good grasp of how deep your DOF is at a given f/stop and distance, and this applies to macro or landscape. A narrow setting will give you a sharper stack, but you may need to take more shots to cover the area you want to capture. It just depends on what you consider "acceptable" focus as to whether you use Narrow or Wide. Wide will move your FP closer to the back of the DOF of the previous FP, so you will start to see some softness. This can be slightly corrected in DPP, but it's a long wait to see the outcome if you have a large stack.
The built in stacking of the R5, and other Canon cameras with this feature, is very basic and sometimes the features are poorly explained. Focus increment is explained, kind of, on page 241 of the R5 manual, actually, it's pretty good at first then they go off a bit, IMHO.
Most of the time I use Helicon for both capturing and processing stacks, but still use the R5 and DPP for smaller stacks. I'm starting to use the R5 more of late and processing in Helicon Focus. Helicon Remote doesn't officially support the R5 and R6, so I am running their beta software, which is a bit hit or miss. But Helicon Focus supports CR3's from the R5(6), it just doesn't export EXIF data in the finished stack.
I hope this helps 🙂
Newton
