I know this is a stupid question but how should the hAP ac2 sit?, vertically or horizontally using the provided stand.

Greetings

It is designed to be positioned vertically...

It is designed to be positioned vertically...

... or horizontally. The supplied transparent stand fits in both orientations.

Given that wifi antennae are all placed on same side of circuit board (top side when unit is oriented horizontally) it has a slight (but really slight) directivity. Use that as it suits ... or not.
I guess cooling is a bit better if oriented vertically as it emphasizes the "chimney effect" causing slightly higher air speed through the unit.

mkx, he said how it is positioned with using the provided transparent stand....

I never use the stand when i place the hap horizontally... it sits perfect without it...

I use it if i want the hap to sit vertically or when i mount it on a wall ( which is what i do at 99.99%)...

mkx, he said how it is positioned with using the provided transparent stand....

I never use the stand when i place the hap horizontally...

Whether you use the stand at all is your personal choice. I'm pretty sure that using some plastic ties you could get the device stay in upright position without using the stand.

The housing is designed such that the stand gets used in both orientations. Hence my answer: device can sit in either position (either with or without stand).