Explaining the ordering of these characters

[Gharial 109]

The Pocket Chinese Dictionary from Oxford (1999, which is basically a revision of their famous 1986 Concise E-C/C-E) states in its 'Guide to the use of the dictionary' that "Characters identical in romanization and tone are arranged according to their first stroke, in the following order: 丶 dot, 一 horizontal, 丨 vertical, 丿 left-falling, and 乙 turning stroke (including 乛 and 乚 )".

But why then are the characters in it that are pronounced bian1 in the following order? 煸 , 蝙 , 鳊 , 编 , 鞭 , 边 .

I'm assuming that Oxford didn't want to break any apparent "phonetic series" (here formed by 扁 bian3) by putting 鞭 between 煸 and 蝙 .

Anyway, it would be helpful in my opinion if Oxford explained their reasoning and/or had more detailed instructions in their dictionaries; as it is, they are, with the exception of the beginner-level dictionary by Yuan & Church (and that is only really suitable for beginning the spoken language - its range of vocab is a bit too small to be of much use in reading at all widely), almost utterly devoid of guidance and training in details (names, stroke orders etc) of radicals, and general looking-up skills.