On the bleeding edge with “eta reduced lambda” functions

Buried in the announcement about New aggregation functions is a reference to “eta reduced lambda functions"; if in the Old Days we had to write:

 =BYCOL(C3:F6,LAMBDA(x,SUM(x))

we can now just use:

 =BYCOL(C3:F6,SUM)

So far so good. This is really a great improvement in both writing and readability.

Being curious, I wanted to see how it works in a named Lambda function. In the Old Days, I would use this:

OldLam = LAMBDA(myrange,  
     BYCOL(
        myrange,
        LAMBDA(col, SUM(col))
    )  
);

But trying to use the new eta lambda style, like this:

NewLam = LAMBDA(myrange,  
     BYCOL(
        myrange, SUM)
    )  ;

doesn't work.

I understand this is all beta, etc., but am I doing something wrong or is it a "feature"?