I haven't figured out all the BCOD flags.
But it usually helps if you look at the flags as binary numbers.
000000000001 1 sector is stair (or ramp)
000000000010 2 sector is bridge
000000000100 4 not enterable by all units (used for fences)
000000001000 8 not enterable by enemies
000000010000 16 blocks sight (used for walls, rocks and buildings)
000000100000 32 (never used)
000001000000 64 climbable wall
000010000000 128
000100000000 256
BCD only:
001000000000 512 ?
010000000000 1024 must crawl (used in BCOD tutorial)
100000000000 2048 ?
often used flags:
000110000000 384 normal sector
000100010100 276 blocked sector
000100000100 260 can walk / cannot see through
other combinations:
000110010000 400 = 384 + 16
000100000101 261 = 260 + 1
000110000100 388 = 384 + 4
000010000100 132 = 128 + 4
010100101100 1324
010110011000 1432
100000010100 2068
The best way to figure out the unknown flags is by changing the flags on an existing SEC and see how the units behave. Is the view cone visible? Can all units walk on it? etc.