Optistruct stress result about use corner data option trun on or not

hi,i am new user for optistruct solver

i have some question(plastic) for the result of optistruct analysis.

my material card use mats1(give the two point "one is yield point and the other is ultimate point" form the curve)

i solve a engineer problem,but when i check the result and i confused.

i know the meaning of hyperview option of "use corner data".

turn on the option mean watch the "node vonMises stress"

turn off the option mean watch the "element center vonMises stress"

my question here

if turn on the option and my vonMises stress result will greater than ultimate strength.

if turn off the option and my vonMises stress result will less than ultimate strength and greater than yield strength.

1.If i want to compare vonMises stress between my result and matweb value.(should i turn on or turn off "use corner data")

2.Optistruct plastic curve should input engineering stress-strain or true stress-strain?

3.By the way,matweb stress is Engineering Stress value or True Stress value?

i really need my qeestion answer,and i seach lots of data but i confused.

so if you are a senior cae engineer,can you take a little time to help me,tks