The Note 3, 4 and 5 were 5.7". the Note 8 is 6.3". That doesn't sound like "shrunk" to me, that looks like "grown".
If you mean the entire case, the Note 5 was 3" wide, the Note 8 is 2.94" wide - 0.06" difference. (Length and thickness remain the same.) Not much - 2%. Probably because the display changed from 16:9 to 18.5:9 - which is where the industry is going - no-edge displays.