The Best Lifted Index from the Eta is derived from calculating the Lifted Index 
from each of the (six) 30 mb thick (approx 1 km) "boundary" layers and taking 
the most unstable or "Best" Lifted index.  This term DOES NOT consider such 
things as the capping inversion which could limit or prevent the convection from
developing.  It is used to help diagnose where the most unstable air is.