Inherited IRA RMD 5yr rule reporting RMD

I have an inherited IRA, and I plan to withdraw the money under the 5 yr rule (which I understand as requiring me to withdraw all money within 5 years to avoid penalties). I calculated the amount I could withdraw (take as a distribution) in 2019 while remaining in my current tax bracket. I believe that amount exceeds what would have been "required." 

 

 On the 1099-R, there is a question of whether the full gross of the distribution should be considered the RMD, or only part of the distribution. I cannot find any guidance about this question. Is there a reason the full gross should NOT be the RMD?