common mode input range for ADC

Hi all , the MCP3302 data sheet says that the common mode input range VSS -0.3V to VDD + 0.3V.
But what I do not understand the figure 5.8
https://ww1.microchip.com/downloads/en/DeviceDoc/21697F.pdf (page 19).


Why for Vref = 1.25V the common mode range was reduced to 4.05V to 0.95V?

I think I figured it out.
Vcm_max = 5.3V - 1.25V = 4.05V. And 4.05V + 1.25V = 5.3V so we can full ADC range.