Exposure Warning and RGB Values

I've noticed a little while ago that increasing contrast in the exposure tab did not appear to affect the brightest highlights (in terms of there RGB values) so I'd assumed that the contrast slider did not affect all values in a proportionate way. However I was just playing around and I noticed that when increasing contrast in areas where marginal highlights go above 250 or so (my highlight warning is 250) the contrast does not affect RGB Values but the exposure warning changes (sometimes dramatically). To ensure I was hovering over the same values i used the apple z / apple shift z command to flick between contrast of 0 and contrast of 50 (i.e. max). The rgb values stay the same while the exposure warning fills the screen. Is there any point in the rgb values if they don't reflect the adjustments?? Lots of people don't like using the exposure warning. Anyone else had this issue? 10.5.8 (I have a process recipie/proof profile selected)

Thanks in advance.