Had a customer spray some beans a couple of weeks ago.  The field had some volunteer corn in it.  And the farmer had some Poast sitting on the shelf.  So, I told him to add some Poast to the glyphosate.  Did not add any crop oil.  It worked well.  As I recall, volunteer corn was about 12" at the time of spraying.

Honestly, I think the Poast will work just fine for you. Whether you want to add the crop oil..... that is your decision.  I do get concerned about using crop oil in this heat.  If using the crop oil, maybe you need to pick and choose when you do this spraying.......