OK, sorry - I thought that by “flattening” you meant the flatten that was being done on .egg load, which isn’t as aggressive as flattenStrong(). In particular, it doesn’t combine siblings unless they are within a certain distance of each other (set by egg-flatten-radius, default is 0).
The or node is there to preserve nodes across even a flattenStrong() operation. You can add a DCS or Model tag to your node by going to the Logic panel, creating a String Game Property called “ObjectType”, and setting it to “model” or “dcs”.
You can of course also just add the appropriate or to your custom object type definitions in your .prc file.