Welcome to the forum.
The search function here provides years of shared information. Here is an old thread which may be where you got the settings of 250/25. Mylar 10 Mil stencils - #3 by ptodd
Since materials are variable, it could be that you will need to adjust your settings and test until you get a good result. If you believe items are melting, increase your speed. There are some very good templates for testing settings in the Free Laser Design section.