Not sure about the exact purpose of R3, but in simulation adding this resistor significantly improves circuits performance. Its value is in the range or hundreds kohms and must be adjusted for different circuit current. R2 is 1Mohm and according to description is needed for circuit start-up.

Not found what is cited here (?).

Here is what I have found ... for T = -25, 0, 25 °C.

My R2 & R3 (same value = ~ 1 kOhm) choose the current.
My R1 & R4 (quasi same value = 5 kOhm) choose the "internal" resistance of the "current" generator ( from ~ 13 V -> 30 V).

Not sure about the exact purpose of R3, but in simulation adding this resistor significantly improves circuits performance. Its value is in the range or hundreds kohms and must be adjusted for different circuit current. R2 is 1Mohm and according to description is needed for circuit start-up.

Not found what is cited here (?).

Here is what I have found ... for T = -25, 0, 25 °C.

My R2 & R3 (same value = ~ 1 kOhm) choose the current.
My R1 & R4 (quasi same value = 5 kOhm) choose the "internal" resistance of the "current" generator ( from ~ 13 V -> 30 V).