Rollei Retro 80s dev in Acurol-N

New to this forum and relatively new to the darkroom, so forgive what may be a newbie questions.

I have used Adox Rodinol since I started a couple of years ago, and MDC for dilutions and dev times, with good results. No stock anywhere in Japan so I decided to try SPUR Acurol-N. And also decided to test Rollei Retro 80S.

Shot the Rollei at box speed ISO80 then checked the MDC for SPUR Rollei dilutions and dev time. MDC gives ISO at 20. That's me confused! Do I simply take the MDC 1+70 for 10-11 mins and ignore the ISO20 part, or do I need to effectively double the dev time to push two stops?

Any guidance would be greatly appreciated...or should I just wing it and see what happens?

The Rollei Retro 80s is Aviphot 80, a high resolution aerial surveillance film. This type of film needs to be given extra exposure, EI=20, to get closer to pictorial contrast negatives. A good explanation is given here for Aviphot 200:

Since you exposed it at EI=80, you have a choice, either develop for the times given for EI 20 which will give thin negatives due to underexposure but pictorial contrast, or push process it maybe 30% which will give near correct highlight density but high contrast.
For some subjects high contrast works well, for others pictorial contrast is better.

Thanks for your advice Allan.
I also tried contacting SPUR and surprisingly got a really helpful reply, within a couple of hours. Thank you Heriburt Schrain!

Heriburt Schain replied:

"To push the Rollei 80 S to ISO 80 /20°, please develop as follows:
Dilution: 1 + 70
Developing time at 20° C: 13 min
Inversion: The first 30 sec permanently, then once every min
The result: no full shadows (zone 1 has a density of 0.03), the contrast is slightly too high (N + 0.5 development), but moderate highlights. "

I did 13 mins, but with a 1 min continuous inversions, then 3 every min. Worked really well, with varying subjects and lighting conditions, although some negs are a bit thin, as you say. I also shot the last 4 frames at ISO40 just to get some comparison. Just scanning now to determine which to print when I get some DR time. I will post my results in a day or so fo anyone who is interested.

Interestingly, I also shot a roll of Kentmere 100 at +1, same subjects and developed in Acurol-N and developed at 1.5x box speed and got good results again. The grain is very different, so it will be fun to compare both when printed.