Setting Over voltage and Under voltage limits for LTC4364
The UV and OV inputs trigger at about 1.25 volts (read the data sheet) so, using R1, R2 and R3 values from your top digram, you get a potential divider ratio at the UV input of: -

(90.9 + 10)/(90.9 + 10 + 383) = 0.2085

So if the input voltage is 6 volts you get 1.25 volts at UV.

Note that your top diagram has "6 V" written beside the UV pin. It doesn't mean that 6 volts appears at that pin, it means that when Vin is 6 volts or below the UV lockout circuit triggers.