OK. If it were standard film and developer, I'd be able to help more...

Did you use a "Tungsten" light source? That might be way slower than daylight if I put 2 and 2 together right about red sensitivity (because Tungsten bulbs are "sort of" on the reddish yellowish side of the spectrum).

Next, I'd seriously develop longer. This could account for less speed than expected. Maybe you'll eventually find your time should be 10 to 16 minutes.

And finally since you kind of estimated the speed at 25 - use that as your Exposure Index to base your calculations for the high "Zones" exposures.