While hunting around for the background on this, I found:
http://lists.ibiblio.org/pipermail/b-greek/2004-June/030424.html
which gives a reasonable overview; in short, yes, there are two variants of drawing the perispomeni accent; either as a variable tilde, or as a invert breve. The determining glyph is '῀' (U+1FCO) which is used as a component for the rest.
While hunting around for the background on this, I found:
http:// lists.ibiblio. org/pipermail/ b-greek/ 2004-June/ 030424. html
which gives a reasonable overview; in short, yes, there are two variants of drawing the perispomeni accent; either as a variable tilde, or as a invert breve. The determining glyph is '῀' (U+1FCO) which is used as a component for the rest.