alpha from long only v.s. alpha from long side of long-short

[hengzh47]

concerning CFAI 2013 morning session Q3 D, it is mentioned that the alpha from long only strategy is smaller than the alpha from long the side in the long-short strategy. I cannot figure out any reason for this happening. The answer only mentioned about the different alphas between long and short, but not about between the longs.
Can someone shed a light on this?

 

[hengzh47]

my bad, it is actually in part E. long in the long-short strategy can free up more fund to exploit return opportunity from the long side.

 

[fakhro]

In a long only strategy you can only overweight stock to a max of 100% of the portfolio. With a long-short strategy you can use your short positions to overweight your long position by more than 100% - for example short 20% and use the funds to go long 120% therefore earning a greater alpha.