Two observations per day, standard approach

4-day campaign   5-day campaign   6-day campaign   7-day campaign
  day  sequence    day  sequence    day  sequence    day  sequence
   1   A  B         1   A  B         1   A  B         1   A  B
   2   D  E         2   D  C         2   D  C         2   D  C
   3   D  B         3   E  B         3   F  B         3   F  E
   4   E  A         4   A  E         4   A  E         4   G  B
  (5)  B            5   D  B         5   D  B         5   D  A
                   (6)  A            6   F  E         6   F  E
                                    (7)  A            7   G  B
                                                     (8)  A

8-day campaign   9-day campaign  10-day campaign  11-day campaign
  day  sequence    day  sequence    day  sequence    day  sequence
   1   A  B         1   A  B         1   A  B         1   A  B
   2   D  C         2   D  C         2   D  C         2   D  C
   3   F  E         3   F  E         3   F            3   F   
   4   G  H         4   G  H         4   G  E         4   G  E
   5   A  B         5   A  B         5   A  B         5   H
   6   D  E         6   D            6   H            6   A  B
   7   F  H         7   F  E         7   D  E         7   D   
   8   G  B         8   G  H         8   F            8   F
  (9)  A            9   A  B         9   G  H         9   G  E
                                    10   A  B        10   H
                                                     11   A  B

In all cases:

  source   times observed    note

  A        2 *               fiducial  *observed 3 times in 9+ day campaigns
  B        3 *               fiducial  *observed 2 times in 4-day campaign
  C        1 *               primary   *not observed in 4-day campaign
  D, E     2                 secondary 
  F, G, H  2                 tertiary

Longer campaigns should insert holes into the schedule; no more than 17
standard observations are needed per campaign.