Hi Dave, because of the Annexe to rule 10.
For a long time the rule regarding kneeling was if you can't kneel then stand. However, I cannot find this written. In 2008 an Annexe was written to rule 10; in the first paragraph "It is neither a new rule
nor an amendment to the existing rule"
Prior to this (implied) a competitor agreed with the Chief Marshal an alternative position if the competitor could not stand or kneel. For example: a shooting rest, or take kneelers standing.
From its adoption in 2008 (probably 2009 season) the adapted positions have now become the default position. For example anyone new to FT who could not kneel would, I think naturally, assume that the adapted kneeler is the way to take kneeling shots. However, this is not the case and such a person could, with the agreement of the Chief Marshal, take kneeling shots standing. Whilst the adapted positions are not the only way of taking shots alternative to the normal stance they are available to be used to shooters who are permanently or temporary disabled hence they use them. Marshalling must be uniform - it is not for one Chief Marshal to allow a position for another to deny it and the Chief Marshal cannot make medical decisions. Such then that if I injure my knee and say to the Chief Marshal I cannot kneel down then he/she cannot say to me "then you must stand" given that anyone else with a knee injury shoots from the adapted position. It then comes to the spirit of the rules - personally if I had a bad knee then I'd stand but as it is if I took up the adapted position I would not be breaking a rule.