In regards to the hitting power of the Ho-103 12.7mm machine cannon, I think HTC has done a great job with it. Poorer armor penetrating capabilities, with a pretty good result on wings and fuselage.
“This combat tends to confirm intelligence reports that state that the Hayabusa's machine cannon, though having poor penetrative powers, had significant explosive effect. A Type 1 fighter that he identified as a ZEKE hit 1 st Lt. Roy Klanrud a P-40 pilot of the 35 th FS. According to Klanrud: “I knew I was badly shot up…I expected another attack which would have been fatal because my elevator and coolant was shot up by a 20mm cannon. Three bullets hit my armor plate and glanced off, clearing out the glass of the canopy on the left side.” More than one American fighter pilot hit by 12.7mm explosive rounds thought he had been hit by the larger 20mm round fired by the Japanese Navy's Zero fighter. A partial explanation for this phenomenon is suggested by findings of Britain's Ordnance Board that tested Japanese army 12.7mm ammunition. A 1944 report said: “The fuse of the H.E./I. [high explosive/incendiary] shell is probably too sensitive for optimum performance.” In tests in India the same type ammunition failed to ignite fuel in a partially filled petrol tin, it was thought because “the blast effect was such that any possibility of petrol or petrol vapour being set on fire was nullified because of this.” Another report concluded the super-sensitive fuse was likely to explode against an aircraft's wing or fuselage skin before penetrating to a fuel tank. Japanese armor piercing ammunition was found to be effective against certain types of Allied armor at least at close ranges on the order of 100 yards.”
http://www.j-aircraft.com/research/rdunn/248th/248th-2.htm