Well, it might be possible to mod this in by setting the proximity charge distance to 50 meters (or in-game units, whatever) and set the blast radius to 75 meters.
While that is a sensible idea for how to set your fuses using the current system, it's still not as good as the thread suggestion.
If this suggestion were implemented, it will always explode at the closest point to its target (or at a set minimum range), no matter if that's 74m or 26m, or anything in between. It's just better than a static fuse that way, which is why it would be a lovely addition.
Even better, if implemented as requested, this fuse system would allow projectiles with varying degrees of 'smart'ness.
A dumb mine could be set to be fused at 50m with a 50m minimum detonation, and it would behave just like the current one - explodes if anything comes within 50m, no questions asked. On the other hand, a particularly smart weapon system could be set to 5m minimum, 500m maximum, and have a huge range of effect - this would be excellent for things which fired a second stage missile at the target, since it would wait until the best shot before firing.