Doesn’t number, placing, and pattern of throw of irrigation heads need to be considered, especially from the long term maintenance and upkeep and cost perspectives?
Atb
Probably less costly to maintain 2 large tee boxes than 5 smaller ones covering same area?
Well, you have to pick up the mower blades 3 less times. Also, each tee needs two yards front and back as the minimum distance away to place tee markers, so five tees are larger, but may not have any more useable space in some cases.
As to irrigation, it is rare that I consider that. Typically, we design for tee space we want and figure the irrigation guy can figure a way to cover it somehow, varying sprinkler size, part and full circle, etc.
As TD notes, it is sometimes hard to put multiple tees, a flat surface on severely sloping ground without losing too much tee space. And, you can't combine them on a downhill slope due to grade and the vision problems of seeing over the front of the forward tees to a downhill green.
As to the original question, most architects know to increase par 3 tee size by 25 to 100% on iron par 3 holes. The back tees, used by good, and bigger divot taking players really needs to be enlarged. Would be interesting to know who didn't know that. it's either a tough site (if one tee) an inexperienced architect, or a contractor who holds more sway over the final product than the architect (and most good ones would also know to make par 3 tees bigger).