Why wouldn't it explode on contact, then the force knocks it offline and the residual blast hits the people in cover?
Also, I think WestRider hit the nail on the head in terms of how shooting attacks are resolved. Technically, all the shots from one unit to another unit would be part of one shooting attack, therefore it would be all or nothing. Meaning, that an autocannon that fires and hits the target unit twice would only get to resolve those shots against the shield in your version, not getting a chance to break through on the first and then resolving the wound on the unit with the second.