Every sleeping bag I've had from past to present, has been a fairly tight fit in its stuff sack across the bottom of my rucksack, and I am guessing that is going to apply to 99% of all rucksacks. (Don't forget to put it in a strong plastic bag to keep it dry.)
As NeilC has pointed out, you can remove the end poles from a Zephyros, although I must admit I find it a bit fiddly to put them back at the end of the day, when I'm tired, have cold hands and it's raining. But it is what I do, and I fold the tent to fit the width of my rucksack. If you leave the end poles in, it is too long, you can only put it in your sack vertically, then you might end up with an imbalance of weight between one side of your sack and the other.
I keep the tent rolled up with a couple of lengths of velcro, which you can buy on eBay, it goes in a heavy-duty black bin bag to stop it making anything else wet (I also use the bag to sit on in the porch, it keeps my backside dry) and I pack it on top of the sleeping bag. The pole bag is slender enough to be poked down one side of the sack, the peg bag is small enough to be tucked almost anywhere. The tent bag stays at home, it still has the swing tags on it, good as new!
