Re-reading the example in the rulebook, I don’t understand the +2 TH DRM to switch target to the 6-2-8.
To me, since the turret is already turned towards BB3 (side facing), the +2 ST change was already paid to shoot at the 4-4-7 (+2+1 = +3), so the shot at the 6-2-8 should only be +1 TH DRM...