I have a fake install of FSX boxed on my machine, but it doesn't get detected with the FSDT installers. Could that be what is causing issues?
Yes, this method, which you surely must have used because of other add-ons not compatible with FSX:SE, should *never* be used by proper addons like ours, which DO recognize and support FSX:SE properly.
FSX:SE has a proper way to be installed to look like FSX, which is the stand-alone mode, with FSX:SE using the same registry keys as FSX. However, this mode won't be enabled unless you remove ALL the FSX registry keys AND run FSX:SE again from the Steam interface, so that Steam could reconfigure it to run in "FSX mode".
With a fake FSX install, you did exactly the opposite, and prevented FSX:SE to run in FSX mode, so it's now probably running in some sort of hybrid mixed mode, which is neither FSX mode or FSX:SE Dual mode, likely because with your fake FSX install, you are preventing to have the Steam program to be able to configure it correctly, and this will cause problem with every 3rd party installer, like ours, which properly recognize FSX:SE in BOTH modes.
- Remove your fake FSX install
- Remove ALL the fake FSX registry keys from the registry
- Run FSX:SE once from the Steam interface, and notice if Steam is saying something about reconfiguring the program on the first startup.