The back of the side plate is actually a c shape groove profile that the strut fits into. It's difficult to find a steel plate that fits exactly in the width of this groove.

Wouldn't flipping this part upside down not really help much since you would have a similar amount of lateral force at the eyelet near the dropout flange? so it would snap at the bottom instead of the top if you did install it upside down.

Edit: actually now that I think about it because of the c shape profile, The bending that it applies to the strut in the direction of travel would cause one side of the hole to experience compression and the other side of the hole to experience tension which might have contributed to the fracture. So installing an upside down would help add strength at that area. On the other hand I see now that the other end is shorter from the hole so may not actually work upside down to counter the bending from the c shape profile.