Define tracking and what sensors. Tracking might not have been the right word. But when the gimbals circle around the sub target you selected to aim at. The difference in radius the gimbal aim reticule points circle were smaller with each upgrade.
Locking on and tracking can be two different things. Tracking suggests some kind of intelligence and following a target under something like AI. Locking on is more like grabbing something and holding on as best as you can till you get shaken off but the computer doesn't use AI to intelligently follow the target. <shrug> What I noticed was just that the aim reticul was noticeably more precise at locking on with Grade A over C and D. And was not as aggressively dissuaded by chaff.
Perhaps you were simply shooting at different ships with different heat signatures? That could explain the different tracking behaviours... I don't know, but I've never noticed any real link between sensors and gimballed weapons tracking accuracy. And I'm at Dangerous rank...