I hooked up my main 3" horizontal drain line so that the downhill end does a "short/small" 90 degree turn slants down again slightly for 2 feet and takes a wye to straight down. I didn't think much of it until I ran across the 1.5" "longer" 90 degree and was wondering if maybe it would be prudent to find a 3" "longer" 90 degree turn and use that in place of my short one. Is it worth it to try and switch to the longer more gradual turn or am I wondering about such a small difference. The 3" pipe drains a kitchen sink, dishwasher and washing machine.
Short sweep 90s are not supposed to be used horizontally. The long sweep you saw is the minimum requirement. A better option, if room allows, is to use a tee-wye combo fitting (a wye and street 45) to make the turn. Put a fitting female adapter on the end with a clean out plug for future access.