I may be wrong on this, but the logic is:
You can buy down an FAP as per the table. If you do this you may split one of the resulting ship/points as per the rule in the rule book: 2 ships at a lower level and spliting only one of those down further.
Example: 1 War = 4 raid (table buy down) = 3 raid, 2 skirmish = 3 raid, 1 skirmish, 2 patrol
Or you may take an FAP and split it down. 1 war = 2 battle = 1 battle, 2 raid = 1 battle, 1 raid, 2 skirmish.
You cannot do the table buy down multiple times.
You cannot split and then use the table buy down.