Why battlecruisers do not lead the line of battle

Would the separate battlecruiser force operate at the front of the line of battle as scouts?

It could perform reconnaissance, but that does not mean placing battlecruisers at the front of the battle line.

Reconnaissance is an operational role rather than a fixed station in a gunnery formation. Battlecruisers use speed to find, shadow, or report the enemy and to support forces away from the main battle line. Putting them at the head of a line would expose ships built around a speed-and-protection compromise to concentrated heavy fire. The distinction helps separate fleet scouting from the tactical deployment used once battleships engage.