Mass Update AND/OR question

I have tried creating AND/OR queries in Mass Update and I am confused by the results. Sometimes it looks like the query runs an and and other times it runs an or.

Is there a way to set which of these the query uses?

My understanding is that when you have two or more criteria on the same field/column name, it is an automatic OR. and the user cannot define or control this
.
So P21 would do:
Description contains Large
OR Description contains Jacket
AND Product Type is equal to Clothing

but not
Description contains Large
AND Description contains Jacket
AND Product Type is equal to Clothing

Hope this helps

Newbie with P21. After working with it more I think you are right.
Thanks