This was taken on SFX through an 89 Filter. At high altitude (4,000 m+) the air is very cold and although plants reflect IR radiation, the don´t give off the glow they show at lower altitudes. Skies, however, can reach very deep tones. This was a sunny day and still air temperature was about 2C
Yes, the Wratten 89B is equivalente to the R72. I expose both, Ilford´s SFX and Rollei´s IR400 @ ISO 6 without filter,
and then I put the filter on and take the photo. The Wratten 89B is almost like taking photos with you lenscap on.
The 72 is the strongest I've used with SFX and Rollei. I use Kodak's opaque 87C on Efke IR and HIE. I'm surprised that you rate Rollei at EI 6 with no filter. I use EI 200. EI 1.5 with the 72...