Targeting priorities

If not, then I've noticed if I use a wall formation my ships often hedgehog (stack on each other) then fire at whoever comes into range all at once. This would often effectively result in targeting one ship.

AFAIK, the only way to get everyone to target a ship is to do so via tactical battles.

I have noticed during simulations (PD heavy ships vs. fighters, big ship vs. many small ships) that based on the settings, will only fire so many shots at a target.
The default for many strategies, iirc, being "Total Targeted Damage" at 150%, so only enough weapons to do a minimal of 150% of the targets structure will be fired at the target.
I don't know if this 'structure' takes shields into account or not.

I don't know if the game has any 'default' value that is used if "Total Targeted Damage" isn't used.

I think (but have not confirmed) range is another factor, so 'leftover' weapons might be aimed at the next closest target, rather than at the next closest target of the highest priority.
Also, I think shots fired at a target take into account shots still 'en route' to a target (such as seekers or 'projectiles'), and only fire enough to add onto the already fired shots fired at a target to reach the 'total targeted damage' limit.

Having everyone focus on a single target could be a waste of firepower. Imagine 100 enemy ships, each with 100kt shield and 100kt structure, and your big fleet decides to pump its entire payload of 10,000kt of damage into a single target, instead of spreading it out.
As is, the "Total Targeted Damage" is a handy setting. Perhaps set it to max (200%?), to ensure as much firepower as is 'needed' is used against an enemy, without wasting all of the firepower on a single target at a time.

I'd rather have salvo leave a few badly damaged or crippled enemy ships to deal with rather than a single dead enemy overkilled into space dust with many intact enemy ships still attacking at full strength.

The only other way I can think of is manually targeting in tactical battles.