The minimum amount of concentrate according Agfa is 10 ml for each 135-36 or 120 roll film (same area).
The real minimum according Mr. Holz von Agfa (contacted some years ago) is 5-6 ml for each mentioned above film configuration. Under 5 ml it will depend on the amount of Black and White area from the negative so in fact you are playing Russian roulette with your film development.
5 ml in 1+50 dilution is no problem in a Jobo 1510 tank (250ml), one film or Jobo 1520 tank (485ml) filled with two films (10 ml Rodinal) and inverse development. 5,5 ml resp. 11 ml is still fitting in these tanks for a 1+50 dilution.
For 1+100 you can use the Jobo 1540 (1510+1530) tank, 975ml volume.
One of the best combination for Rodinal (renamed R09 "one shot developer", "made in Germany" or Fomadon R09 NEW), is with the APX 100/Rollei Retro 100 film. E.I. 80. (10:00 min. 1+50)
Also the Acros 100 on E.I. 64 is doing well (12:00 min. 1+50).
Classical cubical grained slow and medium speed films are in general the best in this Para-Amino Phenol developer. Efke 25, Rollei Pan 25 etc.
Rodinal can be very old and will not fail in development.
Best regards,
Robert
Retro 100 - Rodinal 1+25
Retro 100 - 4 years old Rodinal 1+25