Interesting
I do feel this field in different areas, not really the spine-- In fact quite the opposite :D
But I do remember a reference on Ojas being the Alchemy of all the energies
It might be that, the placement in which you feel the energy the most is where the “resource” of this energy for you, at this very moment, is.
It might change the more you listen to the field or based on the accumulated experiences of the day-to day, etc.
I’d say the Ojas field is often very personalized actually, which is something I have found to be very unique to this field.