Finding position of list items within specific text

Hello.
Im trying to do following.

In specific row of data in Table I have a text:
"A   B C        D     E"

if I manualy count the positions of which each letter starts (counting from 0) i get:
0, 4, 6, 15, 21.

Now In some step I already cleaned this and splited it into a list:
{"A","B","C","D","E"}

Now Im trying to write an Mcode that would give me the same starting posiotions of: 0, 4, 6, 15, 21
but automated since the amount of spaces could change.
I tried few things and nothing helps.

I think the best option is something like:
Table.AddColumn(
Table.FirstN(
Table.SelectColumns( Custom1, "Column1"),1),
"Positions", each
List.PositionOf(Custom2, true, Occurrence.All))

However this gives an empty list instead of list of values.
Can any1 advise on how to find position within text of all values in the list?

Thank you