Math: horizontal delimiters, vertical alignment?

Andreas Stötzner

My question is about the pairs of horizontal delimiters in the 2300 Unicode block. This overview is taken from the UTR#25 (technical report):

I wonder about the difference in the vertical positioning of the first pair 23B4-23B5, in comparison to the other pairs, where the ‘top’ sorts sit below the baseline but the ‘bottom’ sorts sit very high. If that is intentional, I couldn’t find an explanation anywhere, why this is so. It seems illogical to me but I may be missing an important detail. – I also noted that in the STIX Two Math font, differently to the Unicode materials, all top sorts sit on top and all bottom sorts sit at the bottom.

Has anyone ideas about this?