I'm not sure, I like the card, understood everything, then your explanation made me wonder: how come 5 upped shields can counter Lightning? 5 upped shields mean than N is 5, and, given that 5 isn't more than 5, it won't reflect it. May it be that you meant "N or more"? Because, if it isn't like that, it means that you'll never be able to completely stop the damage.
That was my mistake, it should have been 4 upped cards. It would reflect 4 of the 5 damage and 1 would go through.
Yes, you will never be able to fully stop all damage with this shield. On the other hand, no other shield (outside of hope) can get a reduction that high, and NO shield as of yet can reflect non spell damage.
I'm open to changing wording to "N or more" instead of "more than N" if people think that it should be allowed to give full protection. The main idea is that there is a threshold below which it ceases to function.