I guess I don't understand the question...
You can put any value in for lead in/out you want. Depends on what you want to put in there. I myself always put in something like .100" for in/out for a nice clean round number. If I have alot of stock, the number could be higher. If you use a Swept angle, it could be a completely separate number approach. In my opinion it comes down to the programmer and how much/type of movement you want/need for the particular part. (Talking about 2d contour pathes)
If you mean by 'default', you want a those numbers to be something of a standard for you each time you go in there it's "Pre-set", you can go in and Edit the Operation defaults in Mastercam.
If this isn't what you are asking, let me know.
Mike in MN