Revision 7 does not include MOSFET losses.
Generally speaking a reduction in VOR upto a certain point will result in lower RMS current through the secondary. This can result in lowered copper losses and lower secondary diode conduction and switching losses.
Like everything else though, this is true only upto a certain point. As a rule of thumb a VOR of about 100 should minimize your overall losses.
However lower VOR translates to higher primary current... which means you may need to use a larger device in certain cases.

our project has thermal shutdown problems. we work under 290Vac input voltage and 85c ambient temperature conditions. when input voltage is higher like 290Vac, the mosfet rms current is getting lower because of stable output power. in spite of lower mosfet rms current,lnk364's thermat shutdown feature is activated. we think that, the conduction losses of mosfet is not big a problem. the real bigger problem is the switching losses of mosfet. to reduce the switcing losses, i think, VOR value and switching frequency must be low. are we correct?

Yes that is correct. Usually switching losses can be reduced by reducing VOR and switching frequency. Both these actions however will usually increase conduction losses, so its a balancing act for you. The best way to solve the issue is to increase the size of the heatsink on the TOPSwitch.