Using LOOKUP to pull matching data from specific row headers

I am putting together a spreadsheet that pulls the highest entered value from a horizontal set. The sheet also needs to pull the corresponding title of the column in which the highest row value lies.

i.e: Cell R7 holds highest value of set O12:AO12, R7's data shows in M7 as the highest value. L7 would then show the corresponding title to L7, which is located in L1.

I have used the equation: =LOOKUP(lookup_value, lookup_vector, results_vector) in the M column currently to pull the highest values' corresponding title, and it seems to work in some portions of the sheet (what I think is only the Columns O - U), but not anywhere past that. Any ideas as to why this isn't working correctly?

I am no Excel Wizard, and I greatly appreciate the input. I will attach a copy of the spreadsheet I am referring to.


Thanks again in advance for your assistance.