I think it would be ok to make this configurable, the same way the HashMap loadFactor is configurable. At the very least, it would enable us to experiment with different values and find an optimal value. But I don't think configuring the value as a percentage is consistent with the rest of our configuration.

The name is also a bit misleading, I thought with a value of 25% the entry would be split if the size of the new entry is < 25%, but it looks like the entry is split if the new entry is < 75% than the free entry.