Looking good Tony! Nice job on the Atak set.
Karl, all resin will tend to shrink a bit over time...the degree of which depends on how it's stored (temp and humidity), what the mixture components were when it was cast, etc. The zim stuff is prone more to shrinkage because of how thin it is to start with and does tend to get brittle with age...making stretching it with hot water an iffy proposition depending as Tony describes.