Capture request header - truncate from the start (left)?

as per HAProxy 2.9 Configuration Manual: capture request header

<length> is the maximum number of characters to extract from the value and report in the logs. The string will be truncated on the right if it exceeds <length>.

Would it be possible to implement the possibility to truncate the string from the start (left) rather than the end (right)?
Or is it possible to achieve this somehow even now?