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As for your question CA are always just DLLs. Either native or managed. If you want to reduce their size consider removing any business logic that is not related the deployment.
For example in case of managed CA a common cause for excessive size is to have the build script and CA merged into the same assembly. It is not a problem at all. In fact it is a default dependency model for managed CAs. However if you do a lot of other things in your build script then consider splitting build script and CA assembly. See DTF_ExternalAssembly sample for that.
If your problem is with the native DLL then consider the optimizing your code for that DLL.
As for your question CA are always just DLLs. Either native or managed. If you want to reduce their size consider removing any business logic that is not related the deployment.
For example in case of managed CA a common cause for excessive size is to have the build script and CA merged into the same assembly. It is not a problem at all. In fact it is a default dependency model for managed CAs. However if you do a lot of other things in your build script then consider splitting build script and CA assembly. See DTF_ExternalAssembly sample for that.
If your problem is with the native DLL then consider the optimizing your code for that DLL.