inconsistent behavior of eqn bar operator

[Douglas McIlroy]

The two bars below differ radically, although the barred objects have
the same width. The lone A gets a wimpy short bar. (Roman font merely
avoids possible confounding effects with slanted characters.)
.EQ
gfont R
A bar ~~~ "\&A\&" bar
.EN

If you put a bar over a string of As, the length of the bar increases
by the same amount for every A you add, but that amount is not the
length of a bar over a lone A.
This nonuniformity is unfortunate.

I imagine the design is intended to make the n=1 case look like the
customary dictionary diacritical mark for long A. Ideally this usage
would parallel that of other diacriticals, which have special glyphs.

Doug