Are these trees coniferous rather than deciduous? If they are it might help to explain why the greenery doesn't seem to have any more lightness than I'd expect with a normal panchromatic film. Conifers even with Kodak HIE give off very little infra-red for reasons that escape me
With a 25A red you should get a little luminosity, although not that feathery whiteness that Kodak will give and certainly should get very dark skies and white clouds but this woodland scene may not be the best to bring out SFX's qualities.
Yes, the trees are hemlocks.
The whole roll doesn't have much, if any, more lightness in foliage, or dark sky effect than I might have expected with normal pan. I don't know if that was due to overall conditions of the day, or what. I'm guessing that it may need stronger filter than the 25A.
In this frame, I was shooting straight into the sun, so I wasn't really expecting a dark sky effect in this case.
I have used a 25A and on a sunny day I got very dark, almost black skies. Much darker than a 25A with normal pan film. So on a sunny day I am sure you will see this effect. I had taken a picture of the wife in some gardens on the promenade in the Isle of Man when she was standing by some globe lights which were of course off. However they had a glow and the effect was to simulate a kind of brilliant moonlight.
Persevere. I am sure that you'll achieve an IR effect but of course with a 25A it will always be limited compared with Kodak.
With the opaque SFX filter the pictures I have seen do reproduce the "wood" effect. The benefit compared to Kodak is smaller grain the drawback is much lower speed. From what I've read, on a very bright day a handheld exposure at about f5.6 is possible just above "shake" speed.