It *should* be based upon salesfloor priority.
Example, market salesplanners will begin with "01" then a letter designating back or front. So if you have room for 5 front endcaps and room for 8 back, you'll see....
01F 14bd Starbucks 3/5-4/4
02F MealsPF Promo 3/5-4/4
03F 16bd Kellogs CER 3/5-4/4
04F ....
05F ....
Then....
06B SomethingSomething 3/5-4/4
And so on. Every endcap will have a designated priority that you can look up on your adjacency. Typically it "snakes", so if your dry market starts on G21 then 01F will be G21, 02F will be G23, then maybe you have the permanent Keurig endcap on G25, then G27 will be 04F, then you have your cereal ad rot on G29, then your permanent candy end on G31, then bulk on G33, then G35 will be 05F, then G38 will be 06B and so on. On your adjacency, next to every endcap, it'll tell you what it should be...so it'll say "Cereal Ad Rot" right next to G29, or "AsSeenonTV" next to B30 or "Permanent Floor Care" on C38....
Or in the case of market
Right next to G21 it'll say "D120 01F", meaning that it's salesplanner department 120, priority 01F. If your store starts setting endcaps on it's designated priority, it makes things sooooooo much easier. You don't end up taking down salesplanners early accidentally for a new one and you rarely have to try to "fit" in salesplanners where they may not belong. And you can place your usual carry forward saleplanners, or speciality salesplanners where they are supposed to go so you're not constantly moving it around, or it gets set on the endcap with the right dimensions so you're not trying to fit product on shelving it wasn't designed to do it on. This really helps in C and D block as you randomly get hit with endcaps with larger basedecks or smaller heights and there are multiple departments spanning multiple blocks.