Whether they should be labelled mystical or transcendent may be semantics, but one of the points of the worship of the Vithelan high gods is that they don't really respond to "normal" theist worship. Proper worship of the high gods is the rites of Genderatha and Chaquandarath (the priest and priestess of the high gods), and is usually only known by the Vithelan gods.
It's important as Peter M points out though, that there is a "worship mode" for them too.
End of The Glorantha Digest V8 #632
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