4 to 20ma current loops - best power and receiver practices?
Your power dissipation value doesn't add up.  A receiving device only sees up to 20mA current.  The voltage it sees depends on what it does with that current, but if a 250&Omega; resistor is used, then that voltage will be 5V maximum.  5V * 20mA = 100mW.

Worst case the entire loop only gets up to 20mA * 36V = 720mW.  A sender will dissipate this much if it were the only device on a 36V loop and it is indicating full scale (20mA).  This goes down by 100mW for every receiver on the loop that drops 5V at full scale.