Negative splitting is a fine art and very difficult to get right. That's why only 5% achieve it.
Of course an easy way to negative split is to set off 5 minutes slower than target pace and finish strong but that also defeats the purpose of maximising one's potential.
To aim for your potential one must push the limits to see where your line is and every now and then you'll surprise yourself with a strong performance but more often than not you will end up with a positive split. The key is to minimise that positive as much as possible.
Setting off 5% quicker than your estimated target time is bonkers and can't possibly return a best result. It might produce a PB but you'll never know if a negative split would have produced a better time.