The sort order for taxon is provided through the structure of the Organism table, and is based on Kingdom, Phylum, Class, Order, Family, Genus, and Species.  By default sorting is alphabetical within each of these levels. The NHM is beginning to introduce sub-order into some taxon groups, but the fact that intermediate levels are not generally supported means that the taxon order may not be what is required. For example if families in a group are normally ordered by sub-order then this will not be reflected in R6.

A method has been provided a more detailed sort within the NHM levels, which involves adding a weight to each taxon.  The sort order is then by weight/alphabetical within each level.
The maintenance of these weightings is down to R6 users. They are not the responsibility of the NHM and JNCC do not fund their maintenance. If you are concerned about the sort order for particular group, then your help in providing and/or maintaining the weightings would be appreciated.