LNK302-TN design questions

I am working through a design for a 3.3V @ 28mA output non-isolated design using the LNK302-TN part and I have come up with some questions.  

 Per AN-37 the input fusing resistor at this power level should be a 1/2 W 100-470 ohm part.  When I use PIXI and try to input more than 30 ohms I get a warning that VMIN may drop due to high resistance, Increase CIN to ensure that VMIN > 70V.  I have input values of 100, 1k, and 10k ohms but VMIN never changes and is greater than 70V so it appears that the tool does not take into account the value of Rin when calculating VMIN.  What gives?  Why does AN-37 and PIXI give conflicting recommendations?

 I have chosen to use the optocoupler feedback as the design will not tolerate 10% variation of output voltage.  At 3.3Vout a zener diode, as shown in the example, will require excessive biasing current and be excessively temperature sensitive.  I plan to use a TLV431 in place of the zener.  I am going to add a resistor in series with the optocoupler diode to limit the maximum current the TLV431 can pull through the photodiode when the TLV431 commands no more pulses.  Is there a need to limit the current through the phototransistor side of the optocoupler as well?  It is unclear from AN-37 or the data sheet the input impedance of the FB pin.  If there is 1mA flowing through the photo diode there could be anywhere from 100uA to 10mA flowing through the photo transistor side of the optocoupler if the FB pin is a low impedance input.  If the current is uncontrolled it will likely cause the BP pin to discharge below the hysteresis level and cause a restart of the chip.