We are in the process of converting our existing .NET products from separate 32- and 64-bit applications to single "Any CPU" applications. Part of this work is to update the installers to use mixed 32/64 so that the default installation location is the "Program Files" folder irrespective of the operating system. This works fine

If the (old) 32-bit version of the application is installed on to a 64-bit operating system, it correctly (by default) installs to "Program Files (x86)". If you then try to upgrade using the new mixed installer, the default installation folder is also "Program Files (x86)". I presume that this is because it is an upgrade, it is preserving the current installation folder?
Is there anyway to change this behaviour such that the default installation path is "Program Files" in this scenario?
Many thanks,
Ben