Some time ago, I was sitting on a NYC subway train on my way to work. A frum guy approached me and asked if I would mind moving as I was sitting in his "makom kavu'ah" (designated place).
I was astounded. As this was the train's first stop, and the train was empty (it always is at this stop), I told him that there were plenty of other seats and, as I understood, there was no such thing as a "makom kavuah" for commuting on the subway. The guy explained that he recites Tehillim on his trip, and this is a form of davening, and he needs my specific seat. In brief, I didn't budge, and he sat somewhere else.
To simplify my question, I won't address the claim that reciting Tehillim when it's not part of Shacharit or other tefillah would still be considered "davening". Perhaps, it is, but I'll leave that for some other question.
As I understand it, the "makom kavuah" is only in a shul or one's home or some other private dwelling and applies only for tefillah. Regardless, I understand that there can not be a "makom kavuah" in a public place such as a subway where 1st to occupy a seat gets it. Likewise, if you were to daven by sitting on a park bench in a public park, you could not claim that bench is your "makom kavu'ah".
Am I assuming correctly, or can a public spot really be a "makom kavu'ah"?