bris race shapes vs track variant

[lightspeed2011]

I’m wondering if bris race shapes, like track variant, are good unless they’re bad.

Bris says “relative to par”, “average winners time” and 2 points per length
implication is, like speed to par, there should be a baseline for comparison

gulfstream - 8.5 turf

same horse - same track - same distance - same surface

example 1 - 01/2011
call1 - 50.8 - shape -13 (6.5 lengths slow) - means par near 49.5
call2 - 75.6 - shape -13 (6.5 lengths slow) - means par near 74.3
fin - 105.0 - variant -21 (10.5 lengths slow) - means par near 103

example 2 - 04/2011
call1 - 47.4 - shape +8 (4 lengths fast) - means par near 48.2
call2 - 71.1 - shape +11 (5.5 lengths fast) - means par near 72.1
fin - 102.0 - variant -5 (2.5 lengths slow) - means par near 101.5

If I understand this:
looking at call2
75.6 - 71.1 = 4.5 seconds which is reported as shape going from -13 to + 11 (a 24 point or 12 length swing)
using shape of 24, time diff should be between 1 to 1.5 seconds, not 4.5
using time, shape diff should be 8-10, not 24

Anyone know how/why they justify this?