QUERY PLANNER - Indexe mono column VS composite Index

Hello,

My 9.4 database is used as datawharehouse. I can't change the queries
generated.

first index : INDEX COL (A,B,C,D,E)

In case of query based on COL A, the query planner sometimes go to a seq
scan instead of using the first composite index.

The solution is to add a second indexe (redondant)
second index : INDEX COL (A)

In case of query based on COL A, B, C, D, (without E) as well, it doesn't
uses the first index and prefers a seq scan.

I could create a third indexe :
first index : INDEX COL (A,B,C,D)

But I hope there is an other solution for that (table is huge).

It seems that the malus for using composite indexes is high.

Question is : is there a way to make the composite index more attractive to
query planner ? (idealy equivalent to mono column indexe)

Thanks by advance