Since version 9, BestCrypt has allowed creation of Dynamic containers.
Dynamic (or size-efficient) containers, unlike Regular containers, consume less physical disk space than their virtual size is capable of. The space initially occupied by such containers is rather small compared to their capacity. The size of that space grows as files are added. Therefore, the size of a dynamic container is limited by the size of the volume it is created on. As an example, that allows users creating a 40Gb container on a volume with only 4Gb free space.
As for decreasing the size, it is not possible: once the dynamic container has grown, it is never decreased anymore.