Pavan,
I agree, perfect arrow flight is soooo important in penetration and of course the other Ashby 'principles' like FOC, long narrow two blade heads, ect. that were practiced (Howard Hill shot long narrow 3x1 heads, tapered arrows and they weighed 160 grains instead of 125 like many other points from the day) but not published are key as well. A friend of mine had 2 sons that shot two whitetails each with a 20# at 24" Bear cub recurve. 440 grain total arrow weight Easton Axis skinny carbon arrows. 250 grains of point/insert shaving sharp Grizzly 2 blade heads and 12 yard shots at calm deer. All 4 deer had two holes in them.
I'm certainly not advocating this as a general rule, however if you do have a situation where you're using light equipment, get the arrow flying perfect and utilize the published Ashby principles to tip the odds in your favor.