(ive only tried this with terran vs toss)

Dosent it suck when your stuck below a cliff and everything your firing above at you miss 90%of the time well i learnt this thing that can help with that
1. make sure you destroy the enemies expansions below his primary base
2. beside the cliff place 2 tanks on either side of the ramp and marines just behind em so any units that try to come down are toasted

3. get vultures and firebats over and 1 or 2 science vessels as soon as possible make sure you upgrade speed and s.mines for vulture and EMP for s.vessels.

4. bring an SCV (if u dont already have 1 there) and build an enginering bay by the cliff, lift it off so u can see all the terrain above there should if im correct be heap of units waiting up there

5. EMP there units and the tanks will start firing away also get your vultures to sneak through in the confusion and spider mine his probes

6. this should screw his/her defence pretty bad which leaves u to come in and finish him!

CreepColony's Opinion: Even if you can see what is above you, you will still miss 70% (not 90) of the time. But it is sill helpful. And why send firebats and vultures? Use mass tanks in siege mode!