That safe operating zone means with 230v between source and drain, if you slightly turn on the mosfet in it's linear region, IE slightly turned on to a resistance of 2300 Ohms and the voltage between drain and source is 230v, that is as far as you can safely go. Now, I hope you are turning these mosfets almost completely on when switching. IE, on resistance between drain and source will be 0.035 Ohm, not 2300 Ohm, and when the mosfet is on at 0.035 Ohm, what will be the voltage between your drain and source. I don't think it will be 230v, right? That is unless you are drawing thousands of amps of current...
Now, when turning off the mosfet, the resistance between source and drain should be greater than 2300ohm. It should be in the hundreds of megaohms region unless you have a faulty mosfet. Now, with that resistance and 230v between source and drain, will the mosfet be conducting more than, or anywhere near 100ma?
I think you are pretty safe concerning that safe operating area unless you are making a linear amplifier where the mosfet will roast if you try to conduct a linear 100ma continuous with a 229v drop across drain and source.