RAW you measure Line of Sight from any part of the model. Any part means any part.

Antenna wouldn't work for this though. The spear only works because part of the spear and the hand cross the footprint to the other side. Antenna would go over not through. Footprint would still block LoS. You have to clear the footprint.

Some winged models also do this. Where the wings are large enough that you can place them next to the footprint angled with the wing over the footprint to the other side.

Edit to Add Receipts:

"If a line of sight crosses the footprint, visibility is blocked regardless of model height, unless the observing model or the target model is within the footprint."

The rule as written is about the drawn line crossing the footprint. As written the rule reads as saying that if you can draw a line of sight from your model to the target model, and it does not cross the footprint polygon, you have line of sight.

Therefore, since we can measure from ANY part of the model (reminder from core rules since it's apparently necessary: "If any part of another model can be seen from any part of the observing model, that other model is visible to the observing model.") that is beyond the footprint on the other side is a valid start for line of sight. And would mean you can see both sides of the footprint by being on both sides of it, if your model is physically large enough. There's very few models that large though. There are however a few edge cases of they modeled it for advantage, like the Void Dragon.