I have found recently that a 4-1 defence has lost its effect against narrow attacking formations (4-3-3, 4-3N-1-2, 4-1-2-1-2 Narrow Diamond, etc). My 4-5-1V default formation used to eat those alive, but now a narrow defence (3N-1) with 2MC or 3MC is a lot better.

So nowadays I use 3N-1-3N-2W-1 against 4-3-3 and 4-3N-1-2, and 3N-1-4-2, 3N-5-2V or 3N-1-2N-3AMW-1 against Narrow Diamond and others.