I've never seen an analysis like this before, but agree that it makes sense.
The point being that production, processing and transportation of natural gas results in greater carbon emissions than from the actual end use combustion.
Likewise, in the case of liquified natural gas, liquefaction, tanker transport and regasification result in additional emissions which push to total to more than than of coal.
But now consider the politics... Who is going to be responsible for the offshore carbon emission? The exporter or importer?