Each can be found at any distance from the vent although the names imply otherwise. Proximal-type 'a'a flows tend to be 1-3 m thick, fast-moving, have thin layers of spiny clinker, little fine material mixed in with the clinker, and their interiors are often vesicular. When moving, the pasty interior of proximal-type 'a'a flows can be observed deforming and flowing, and can be penetrated by a thermocouple or viscometer.
To the right are examples of proximal-type 'a'a flows. In A, the incandescent core could be seen deforming as the flow advanced at a few meters/minute, and if you had been properly protected from the intense radiant heat you could have scooped out a pasty blob with a hammer. In B, note that the top clinker layer is only 10-20 cm thick and that the interior is relatively vesicular.