The pump vendors make performance charts that tell you how much air each model will deliver at a given backpressure (psi, meters of water depth, bar...etc.).
I use 1" pipe to deliver air to the air domes. Since is air is far more fluid than water, I know than all the backpressure on the pump is the 8' of water depth...not pipe restrictions.
Remember that any device that measures pressure...much add backpressure. Just like a voltmeter is actually mearuring current.
