My experience with asparagus is that it travels -- one season's stalks often come up 12-24" from the prior season's

It should, since asparagus is more of a mass planting anyway. Put in 6 crowns in a 3-2-1 pattern and they should be fine. Just be aware that the ferns get tall, this should be on the north-ish end of the beds. If it is anywhere else, plant strawberries there instead.

Per U of AZ Intensive gardening guide, asparagus can be space 15 - 18"

Here is a link that might be useful: U of AZ

15 inch spacing is fine, I staggered mine and got more into the bed that way, a couple of extra plants never hurts. It matters more what the soil is sandy but rich loam

Plants don't care what shape the bed is. :-)

CloneZero