1
general::
Phrase(s): set something at something
to fix something at a particular value or amount. • Please set the thermostat at a lower temperature. • Who set the refrigerator at freezing?
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, set upon. Attack or assail, as in The dog set at the postman, or The hyenas set upon the wounded lion. The first term dates from the early 1400s, the variant from the late 1300s.
American Heritage Idioms