Well, let me preface this by saying that I've never pored ganache over fondant, but honestly, it sounds like your problem was with the ganache, and not the fondant/ganache combo. I really doubt that ganache would have any problems over fondant, but I could be totally wrong, lol! I do make a LOT of ganache pour cakes (over cream cheese and SMBC), and I'm big on details, so here's what works for me. YMMV
How warm/cool was the ganache? It doesn't matter too much what your cream to chocolate ratio is (well, it matters
, but less than temp.), and for the record your's sounds like plenty of cream. The key to getting nice thin ganache drips is the temperature of the ganache when you pour it. It needs to be just right, and you'll probably need to do some experimenting to get it right... I don't think I can describe what the right consistency looks like...
Too cool/thick, and your ganache won't drip well. It will be clumpy, with wide, short drips. Sounds like what happened to you. Too warm/thin, and your ganache will pool right to the bottom of the cake, and you won't have any of those nice drips that stop half way down the side of the cake.
Finally, the method
you use to pour the ganache on the cake can be really important to getting the nice, pretty, even drips. I do it two different ways, depending on the look I'm going for. I imagine there are many other ways... these are just the ones that work for me:
First, if I'm going for a drizzle over the edge look, I put thinned ganache into a piping bag with a med/sm round tip (6 maybe?) and just kind of zig zag the bag over the edge of the cake without stopping. I learned this from video posted by another CC'er but I can't find it, or remember who posted it.
The other ganache dripping method I do (way more often), is where ganache is covering the whole top of the cake and dripping down the sides. I use a spreadable ganache recipe that's usually at room temp, and not at all pour-able; so I start by re-melting some ganache in an liquid measuring cup (I like the handle and pour spout). Not for too long either! Go in 10 second increments, stirring a lot between cycles.
Then pour a med-large puddle on the top of the cake. You do NOT want it to start pouring off the edge of the cake (that would be too much), but you want the puddle to be big enough that you don't need to pour more (if possible; cleaner lines with one pour). If I had to guess, I'd say I use about 3/4-1 cup ganache on an 8" cake? I never measure or pay attention though so that could be way off...
Then immediately grab a small spatula (I only use a tiny, round tipped, off-set) and start pushing the ganache over the edge a little at a time, in sections 3/4"-1 1/2" apart. Vary the amount of ganache that you push over the edge to get drips of different lengths. This way you'll have some
ganache covering the top edge all the way around, but drips every 3/4"-1 1/2". Varying the length and spacing makes it look more random, like all you did was pour a bunch on and let gravity do the work. HA!
It's never that easy!
But maybe I'm just a perfectionist... yeah.
Edited to fix typos and clarify a few things.