On all modern motherboards (no matter if it's AMD or Intel or even if it's a server motherboard) you have to use 2/4 slot counting from the CPU side (or 2/4/6/8/10/12... on server motherboards), so almost always marked as A2/B2 (on servers are usually only numbers). It's because motherboards see these slots as first and if you use 1/3 slot (counting from the CPU side) then in some cases it will work, but in some won't boot at all. 2/4 (or A2/B2) are also supporting higher memory frequency, or saying in other way, are overclocking better. In short, if your motherboard supports max DDR5-7200 then it will work probably only on slots 2/4 (A2/B2), and slots 1/3 (A1/B1) will run at max 1-3 memory ratios lower. As a result, if you use 4 memory modules then they will work at max of the slowest slot (typically B1).