FGDB is the % maximum sugar yield of a specific grain/adjunct on Fine Grind Dry Basis. MC is moisture content.
According to
this page, flaked corn has maximum yield of 84%.
Type in 84% for FGDB, and 4 for MC ... and 37.3 will appear in the ppg section. Note the PPG of this adjunct has a range of 33-39 on the HTB link.
HTB doesn't really specify the grind setting to any accuracy, so the calculation falling into range is good enough for me.