[exim] Argument Size Limit with "-be"

hello,

while trying to test some larger expansions using "-be"
exim complains about this:

$ exim -be '${lc:'"$(printf 'X%.0s' {1..300})"'}' ;
exim: length limit exceeded (306 > 256) for: recipient

this ${lc:} expansion is only for demonstration of feeding
"oversized" arguments into exim.

the documentation does not mention any size-limit for "-be",
and there is no recipient involved as the error suggests.

how to use expansion strings with >256 characters with "-be" ?

using: Exim version 4.94.2

thanks,

nico