I'm not sure if there's anything unusual about the C-25, but I know the C-16 and K-27 had thicker pedestal binders under the blind drivers that kept them suspended slightly off the top of the rail. On my K-27 I filed them down and took out the middle one of the three springs from the top of each journal, which allowed the springs to compress more and the weight to distribute evenly across all four driver sets. On the K-27, that ended up being a problem because the trailing axle was bottoming out on the rollers before the driver springs were fully compressed, so the trailing axle was carrying too much of the weight and taking it off the drivers, so I put the middle springs back in for the rear driver pair and that solved the problem (of course there are no trailing wheels to worry about on the C-25, so that won't be an issue for you). As I made adjustments I tried sliding an index card under the wheels. The less weight the wheel is carrying, the more easily the card will slide under it. The goal is to try to get more or less the same resistance under all of the driving wheels. The pilot wheels should carry just enough weight to keep them on the track.
rwjenkins has it right...back when the Accucraft K27 first came out there was a good bit of discussion about adjusting the pedestal binders and/or springs to obtain not only weight being carried by all drivers, but also equalizing the weight among the drivers. Loco balance also comes into play when sorting this out...I know on our Accucraft C19 we added a good bit of weight in the cab to improve weight distribution among the drivers on that engine.
Ideally of course would be a functioning equalized suspension....there are a number of Aster engines that have this feature but alas, none of the Accucraft narrow gauge engines come so equipt. Our David Bailey K27 has functioning suspension for the drivers...it is a thing of beauty and goes a long way toward achieving equal weight distribution over the drivers: