I see. I will give it some thought. I understand your position. But I don't think I'm in agreement.
See, bots will still try to build the ghosts being planned and will wait indefinitely for the cliff explosion to arrive. If you're not paying attention. You've suddenly lost of your inventory's bots without realizing.
Also, I rely heavily on the game's force-build rules. I don't check what's blocking the position. I just ask the API if something can be built. And it takes the research into account for me. So if a position can't be built, I would have to run additional tests why not. And if that happens to be a cliff, ignore it. It's a bit of hassle for still a sub optimal outcome. So I never did.
I might consider keeping the planning as is, but not cancel the plan. Just omit the resources that can't be reached. Plan the ones that can be reached, and prompt a warning. It'd plan around cliffs if able, though. Things might look a bit wonky, but it'll work just fine.
In the meantime you can also consider selecting less of the geysers, and keep the selection clear from the cliff. It shouldnt make that much difference between manually adding. Or manually removing a couple of geysers.