ambiguity in delay of game rules

Rule 13 A5b:

After 20 seconds have elapsed, a defensive player in position at the
spot the disc is to be put into play may restart play by announcing
"delay of game" and may initiate and continue the stall count. In
order to invoke this rule the marker must give warnings of twenty,
ten, and five seconds.

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   Suppose the disc is in a team's own endzone. They have two options
of where to put the disc into play and thus it is not known in advance
which is "the spot the disc is to be put into play". So where should
one go on D?

    Also, can the delay countdown start before the player is in that
position?
It seems that the answer is yes as the rules only say that the marker
must be in position in order to restart play and initiate the stall
count.

    Since the defence does not know who will pick up the disc on
offence and may wish to maintain certain matchups, could they have
more than one player give the countdown and then choose one at the
last second to start the stall count?

,Bob Koca