In line with the point Nathaniel raised - I'd be applying the MPE fix to the whole hand (per the IPG).
That said I don't see massive opportunity to abuse a 4 card fix. The only example I've seen is when playing a combo deck and the first 4 cards include the combo pieces and you somehow know the next 4 will contain another combo piece in the hopes of gaining an extra land…that feels a bit of a stretch.
In any case its a high risk low reward cheat that relies on taking warnings to gain the advantage of letting your opponent make the sub-optimal choice in the thoughtseize. At this point you're also giving them extra information about what's in your deck, frankly just drawing 8 seems a better way to go if you're going to cheat deliberately.
Now, what made me not think it feasible was the fact that given this policy, it's always correct to draw cards in smaller subsections. Doing so will result in a less impactful fix if you get it wrong (accidentally or on purpose).
Drawing cards in smaller numbers actually enables your opponent (and you) to catch errors more easily so I don't want to discourage that behaviour in any case, it's also the reason some players confirm draws or draw cards to the table first before adding them to the hand.
My main concern isn't cheats though. It's perception. If I as a player get a thoughtseize on my 8, it sucks but makes sense. If I then next round have an opponent who draws in piles of two, the Judge will tell me I get to
thoughtseize 2? Regardless of the logic of it, I'll feel cheated by the fix and the judge. Like if you have such an intimate understanding of the policy then you can reduce the damage of the fix…Why don't I get to see all 8?
Better understanding of the rules and penalties allow players to act in ways that make mistakes less likely and to mitigate the impact of such - this to me seems fair.
The fix isn't meant to give anything to the NAP so the whole ‘I should get to thoughtseize from more cards’ argument holds very little weight for me (I think it actually starts to drift into USC minor). The fix is meant to ensure the AP can't gain advantage from the extra cards drawn - and as we know that extra card is in the smaller set (which the NAP will have had to confirm) we only need to show the NAP this smaller set to avoid advantage.