Assembly.LoadFrom(...) is relative from first executable

So I have made an updater for my application. It downloads my application (a .dll file) tp %appdata%/Folder and opens it via reflection like this:

var appdataFolder =
        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + @"\[ApplicationName]\";

var mainAssembly = Assembly.LoadFrom(appdataFolder + @"TF2Callout.dll");
mainAssembly.GetType("TF2Callout.App").GetMethod("Main").Invoke(null, null);

This opens the .dll and executes the static void Main. But in my application I have this:

Assembly.LoadFrom("SomeOtherDll.dll");

I would expect the application to search for the .dll in the %appdata%/[application name] folder because it is saved there, however, it tries to find the file in the folder of the installer, which is in my program files.

How would I go about fixing this? I would rather not make the SomeOtherDll.dll get loaded from an absolute path, because it might change.