  We probe the small-scale absorption line variability using absorption depth
based analysis of a sample of 64 ultra-fast outflow (UFO) C IV broad absorption
line (BAL) quasars monitored using the Southern African Large Telescope. We
confirm the strong monotonic increase in the strength of variability with
increasing outflow velocity. We identify regions inside the BAL trough for each
source where the normalized flux difference between two epochs is $>$0.1 for a
velocity width $\ge$500 kms$^{-1}$ (called ``variable regions"). We find the
total number of variable regions increases with the time interval probed and
the number of BALs showing variable regions almost doubles from short ($<$2
yrs) to long ($>$2 yrs) time scales. We study the distributions of variable
region properties such as its velocity width, depth, and location. These
regions typically occupy a few-tenths of the entire width of the BAL. Their
widths are found to increase with increasing time scales having typical widths
of ~2000 kms$^{-1}$ for dt $>$ 2 yr. However, their absolute velocity with
respect to z$_{em}$ and their relative position within the BAL profile remain
random irrespective of the time scale probed. The equivalent width variations
of the BALs are strongly dependent on the size and depth of the variable
regions but are little dependent on their total number. Finally, we find that
~17% of the UFO BALs show uncorrelated variability within the BAL trough.
