Define two names
Name: aCells
RefersTo: =Sheet1!$A$6:INDEX(Sheet1!$A:$A, MATCH(99E+100,Sheet1!$A:$A), 1)
and
Name:bcCells
RefersTo: =Sheet1!$B$6:INDEX(Sheet1!$C:$C, ROWS(aCells)+5, 1)
Then the formula becomes
=SUMPRODUCT(--(TEXT(aCells,"mmm")=$E10),INDEX(bcCells,,MATCH(F$5,$B$5:$C$5,0)))