The targets may be falling back to the ground. You might have to use a setpos loop to keep them in the air. Alternatively, place them faraway and give the tanks a reveal command.
If sabot doesn't work use heat - it will look better anyway. Changing the explosion at the other end is possible, but would be hard work. You'd need to use a nearestobject command to grab the shell as it left the barrel, delete it and then create an explosion where it should have landed. What do you want bigger bangs for anyway? Where is the player in all this - what is he actually going to see?