Hi Just2Bad,
Yep that barbed fitting goes to a smaller hose because the Sen900 feeding it from the tub has a 3/4" outlet. If I had hard plumbed it I would have done as you suggested.
If you'd like to send me an Ampmaster or other 1" outlet pump, I'll be more than happy to correct those photos for you.
The assumption for the flow would be more realistically based on the flow the pump could deliver rather than plumbing size.