Isn't this a very bad idea?

Using a spacer to offset the track sprocket/freewheel if your chainring sits further out than what matches the hub? I’m quite sure this is a good way to chew your (threaded) hub…

CNC SPACER KIT for Screw-on FIXED TRACK COG Freewheel | eBay

Nothing wrong with it really. Some cogs have less threaded material meaning that once the cog is hard up against the hub the lockring will not come up against it to lock it in place. I have made a spacer myself for this exact purpose.