[Loolasant]

I'm trying to find an image of it

When in doubt it is always a good idea to check Scarbsf1's Blog | Everything technical in F1
Here is his diagram of what Red Bull was doing with their floor.




He has a very detailed explanation of how these holes offset "tire squirt" and illustrates how this woudn't work if the holes were open ended:


Having introduced a “tyre squirt” slot into the floor ahead of the rear tyres at the Bahrain GP, Red Bull had completed two complete GPs before rival teams raised questions about its legality. On the morning of the Monaco GP, several teams started a discussion regarding the slots legality, as it did not follow the practice of Sauber or Ferrari in linking the hole to the edge of the floor. No formal protest was made, but the Technical Working Group (TWG) wanted the rules around holes in the floor clarified. To read the entire article go to the link I provided at the top of this post.

Having a bad tyre squirt effect will rob the diffuser by as much as 50% of its flow, getting it right merely maximises the potential of the diffuser. Having a slot to negate tyre squirt will gain some downforce and hence lap time. Cheaters