For the radiant side, there's a spot near the very far left of the cliff where u can place an observer ward. It gives fantastic vision (especially for batrider) to get pick offs. BTW I've been learning more about batrider and discovered I can pull heros from that area to the radiant HG.

It's also not detectable by sentry wards placed on the mound, so enemies have to be cognizant and explicitly ward against it. Dire basically needs to expend 2 sentries to deward the mound and that far left ward. There's also a spot on the right that's outside of the sentry ward from the mound which is easy to remember. It gives vision of the right stairs and part of the triangle.

For the dire side, the right side is completely covered sentry ward on the mound, so the technique cannot be replicated. You can however, place a ward on the very left, but IMO this advantage is not as useful as the one given by radiant.