HE fragments from the Breda-Safat 12.7mm are capable of causing damage to aircraft many meters away from the blast site. Very impressive for a shell that contained just 0.8 grams of PETN!
I haven't tested it, but the Soviet UB 12.7mm and other 12.7mm MG might also have blast radii which are too big.
While it is possible for shrapnel fragments to travel a great distance, due to their small size and poor aerodynamics they quickly lose velocity, making it incredibly unlikely that they'd retain enough force to inflict damage on an aircraft more than a few meters from the blast.
Edit: Realistically, using a blast radius calculator found here:
http://www.un.org/disarmament/un-saf...ngery-bulmash/
the Breda-Safat 12.7mm HE round (.8 g PETN filler) should have an effective blast radius of a little over 1 meter, since that's the maximum range at which you get 14 kPa of overpressure. Maybe 2 m maximum blast radius to model fragments.
By contrast, the 30mm minengeschoss Ausf.C round with 72 grams of PETN should have an effective blast radius of about 4.5 meters, perhaps doubled to 9 m. The MG 131 13mm HEI-T round, with 1.4 g of PETN should have an effective blast radius of about 2.7 m, perhaps doubled to 5.4 m.