Different animal, but when I had irrigation for a strawberry farm I had a 3" fire pump to feed 3.5 acres of overhead sprinklers. At first I had a 3" suction line to feed the 3" pump, max lift about 8', then it pushed water thru a main trunk of 4", then gradually it got smaller until the ends of the lines were 2" pipe. I had issues getting good enough pressure to the ends of the 2" lines and they were only feeding 6 sprinklers at 60' spacing. I called the irrigation company to see about getting a bigger pump. They said all I had to do was change the suction line to 4". I did that and the pressure and spray pattern was good throughout the entire system.
On vacuum you need to think similar, one size up often performs far better.
Steve Childs, Cornell Maple Expert, has a notebook that shows the performance of various sizes and lengths of tubing. If in doubt, consult that.
Personally I often use 1 size larger, if a pump has a 1.25" take off, I step it up to 1.5", if it has 1.5" I step it up to 2". But then you need to take distance into account, on long runs you may need even larger to get the best performance to the end.