http://scriptsource.org/ws/btt-Latn/sym is inconsistent and might be incorrect.
The diacritical marks indicate tones. It’s more probable that every tone exists in combination with any vowel unless there’s a specific grammatical or morphological context where this can’t happen.

However at the moment
acute-macron U+1DC5 and macron-grave U+1DC6 is only found in
<0061, 1DC5> a᷅
<0061, 1DC6> a᷆
<0065, 1DC5> e᷅
<0065, 1DC6> e᷆
<0131, 1DC6> ı᷆ <-- clearly a error, it should be <0069, 1DC6> i᷆

For every other tone mark (acute, macron, grave, caron, circumflex), a combination with every one of the vowels (a, e, i, o, u) is listed.

Do i-acute-macron, o-acute-macron and o-macron-grave, u-acute-macron and u-macron-grave never occur in Bete-Bendi?
<0131, 1DC6> ı᷆ is clearly an error as there is no U+0131 used in Bete-Bendi.