This isn't like b&w infrared film, you don't use an IR pass filter as you still need to expose the other colour layers.

With a yellow filter on, blocking out the blue light which all layers of the film are sensitive to, the film is still sensitive to green, red and infrared light. After processing the infrared is displayed as red, the red as green and the green as blue. This means that the green leaves of trees and grass which also reflect IR light show up as a mixture of red and blue (magenta).

With a red filter on both blue and green light is blocked, the film will only be picking up red and infrared light. The film will only see the IR light from the green foliage and it should end up red rather than magenta.

Anyway this is rather beside the point but was just to emphasise that. This film doesn't need an IR pass filter like an R72.

The yellow filter is standard to block the blue light otherwise all layers are overexposed. This is taken into account with the box speed of 400 iso with a yellow filter. If I use the red filter instead which has a 1.5 stop difference to the yellow one, was I right to effectively rate it at 150 iso?