When you plot volcanism and flows at the time of large known meteor impacts on
paleo-geographic maps, circles appear at appropriate distances from the impact
site suggesting exactly what you have, that these are far-field effects. Look at
Mare Orientale on the moon, for an excellent example. The same phenomena
has been observed around Mars craters.
The Colombia basalts formed at the same time that a large crater (The Ries crater)
was formed in Germany. This is one of the largest recent impact structures and
has been dated to 14.8 MYBA - exactly the same time as the initiation of the Colombia
volcanism.
As for the Deccan Traps, they formed over a very brief interval between 66-67 MYBA.
This does correspond very nicely with the destructive impact in the Yucatan. Even more
impressive from a triggering point of view is that on a paleogeographic globe of the
time, the Deccan Traps are exactly antipodal to the impact site in the Yucatan.
Waves tend to converge at the antipode of an impact and the strongest seismic effects
are expected at that locale. Two good examples of this are again, the Mare Orientale
on the moon whose antipode is a very strange mottled terrain. The same feature can
be seen at the antipode of the largest crater on the planet Mercury - Caloris crater
has mottled terrain at it's antipode.
The traps of 250 MYBA also correspond in time with a series of extinctions and
known meteor impacts, but I'm not sure offhand where these took place.