The portulaca border is (mostly) stunning.
On to the mostly bit: where the gate path drops a half step, the portulaca is decidedly not thriving.
The stunted plants look healthy other than their relative size. There is no indication of overwatering, even less considering the slope continues downward past the path end.
The division line represents two stages of planting. The first is the stunted bit, and I mostly used existing soil with just a bit of ammending. The upper part of the border was filled in with new topsoil and a more complete ammending mixture.
I am wholly stunned by the difference.