If your only goal is getting the trash under ground then just as shallow as will do it is OK.  I tend to plow deep.  We are running 5-18" bottoms and I figure on a minimum of 9".  10-12 is better.  But we are not plowing for trash, but to stir and break up the soil.  That is one of the reasons we use "Deep Suck" plow shares

I had forgotten how much difference it could make.  I bought a second plow a few years ago for parts and never used it or took any parts off it.  When we decided to plow the 80 this fall we used it and "Old Faithful" I'd dragged for 33 years.  The "new" one had regular shares instead of the deep suck like we always buy.  In the heavy end of the field, where the creek flooded this summer, the regular shares would not penetrate.

Anyway, all that for this:  If all you want to do is clean the surface, just run 4-5 inches deep and do that.  But if your goal is mixing and stirring you better go as deep as you can.

edit: It has to be the keyboard making all these typos.  Couldn't be wonderful me.