411A:
I humbly kneel before the temple of total aviation knowledge however is it not the case that the Jeppesen symbology used to indicate the siting of transmissometers not also indicate their respective orientation?
In other words, a runway served by ILS and RVR in each direction will have its touchdown meter aligned with the relevant runway and the midpoint (if installed) will usually be aligned with the predominate landing direction. Thus the stop end reading will be from the opposite direction to the landing. Bearing in mind the above, substitution of the mid point for the touchdown may be quite appropriate.
Toodle-pip! Old boy!!