It is a bit unreasonable. Your climate is a big issue. Western conifers (with the exception of Ponderosa pine) have a difficult time adjusting to the humidity and wet of eastern summers and the wetter winters--precipitation in the high deserts and elevations out west falls, and stays, as snow). Here in the east, we get freeze, thaw, cold rain, melting snow all winter. It's tough on roots not used to all that moisture.
Most western conifer species evolved in climates that are extremely cold and arid, or extremely hot and arid. The National Arboretum in Washington has had big problems with Western collected junipers in particular. They almost lost some notable California juniper bonsai basically because there is too much rain and humidity in D.C.in the summer.
Size has absolutely nothing to do with a tree surviving, well, I take that back. Smaller trees with smaller root masses are the first to die off. There is less room for error the smaller you get with bonsai. A smaller tree is more apt to die because of a watering mistake than a larger one--not as many roots and not as much soil in smaller pots.
.
