LT1935 thermal resistance and maximum junction temperature does not agree with application circuit

Hello ADI.

I am considering the LT1935 boost DC-DC converter for a new design.  My question pertains to the typical application shown on figure 1 of the data sheet.  See the circuit pasted below.  Vin=5V, Vout=12V @ 600mA.  From the curve, efficiency=87% at 600 mA.  Data sheet page 2 lists max junction temp=125C and SOT23 thermal resistance (Rja) = 113C/W.  For figure 1, I calculate Pout=7.2W, and Pdis=1.08W.  Assuming Tambient=22C, and Rja=113C/W, Tj=22C + 1.08W*113C/W = 144C.  Since 144C > 125C, this would cause the LT1935 to fail. 

My question is: Does ADI expect the PCB copper connected to the LT1935 ground pin to lower the thermal resistance down much lower than 113C/W?  To be comfortable using the LT1935 at 22C with the figure 1 circuit, I would want to keep Tj=100C max.  In that case, Rja=72C/W or lower.  If you agree, how do I calculate PCB copper area required to achieve Rja=72C/W or lower?  Thank you.