Mandyrob
Apologies, misunderstood your query.
Numbering the columns and rows according to the preamble and then noting where the missing letters are in the grid (in the order noted in the preamble) should give you a set of numbers (with decimal points according to preamble (2.4 and 3.6) totalling 15 to match the 15 letters removed).
As others have noted, these coordinates will take you to where you need to look