How hard is IFoS compared with CSE?

In God we trust; all others must bring data. So here it is.

Every year, 30 to 40 IFoS officers attempt CSE. Most clear the Prelims cut-off easily, because they are good at Prelims. But in Mains, not even 20% of them clear it. And in the final result, the best rank usually comes in the 500s, with hardly 4 or 5 selections, most around ranks 800 to 900.

So candidates who clear IFoS with ranks under 20 to 30 find it difficult to clear CSE.

Corollary: you need the writing skill of someone just clearing the CSE Mains cut-off to clear IFoS with a good rank and cadre.