I have a lot of bulbs and not much garden. How many narcissus have you been able to cram into a square foot?
It depends on how long you plan to go before you have to divide them. I plant mine 6" apart, which is usually what the packages recommend. That way, the clumps can get pretty big before you have to lift and break the bulbs apart to keep them blooming. How many years before they get to that point depends on cultivar, soil type and depth.
If you were to plant them closer together, you could, and it would look nice and full the first year or so. But the bulbs will divide into clumps and become crowded sooner, and then you have non-blooming bulbs and more work on your hands.
I could see doing this if you expected to have more beds ready in future years to replant the divisions into. But if not, you're just making more work for yourself in the long run.
Planting deeper and in heavier soil will slow down bulb division slightly. Hope this helps you. Hey... you could always plant them in the lawn, and have an excuse not to mow it until June!