As a slush reader, I have to say I appreciate it when authors read the guidelines. It's a waste of everyone's time when they don't. But I'd also like to point out that the guidelines deliberately avoid giving a positive definition of SF. They give a negative condition - it shouldn't be fantasy or horror. Now, horror is a matter of tone, not content - a story involving robots and spaceships may be better suited to pseudopod if it's meant to tap into some sort of existential dread. Whether or not a story counts as horror is a subjective question, then. It's up to the author to decide and then up to the slush readers and editors to decide whether they agree. The line with fantasy is about content, but it too has a massive grey area. If your story makes explicit reference to the supernatural, then it's probably not suited for EP (though exceptions have been made). If it doesn't, it's again a matter of the author needing to make a call.
Put it this way - if you're genuinely unsure, submit. Worst case, we'll say no. If we really like the story but think it belongs in a sister podcast, we'll probably tell you that. But a more pertinent question is (and this is directed at all authors, not you particularly) - if you're not sure yourself, why not? Is it really a case where they story lies in the borderline between genres, or have you simply not spent enough time thinking your story through? If it's an old story you wrote years ago and it's no longer fresh on your mind that's one thing, but if it's a recently written story then I'd say 95% of the time if an author doesn't have strong opinions about what their story is about, then the genre issue will be the least of that story's problems.