Cheney drank after the incident; to cover up drinking earlier?

According to CNN:

Armstrong had previously told CNN that she never saw Cheney or Whittington "drink at all on the day of the shooting until after the accident occurred, when the vice president fixed himself a cocktail back at the house."

As speculated here, could this have been an attempt to cover up having drunk earlier in the day? Just how big of "a beer" did Cheney have at lunch?