Told you it would be easy!
Throughput you mention is about 60 gpd, so about 60% of rating if you're using a 100gpd membrane. That's actually not far off the mark. We don't get 100% of the rating through these things anyhow, but it is a function of a couple of variables. The most obvious is the household pressure. If you have a pressure regulator on your house (seems to me a lot of newer houses have this), it will dial down the capacity of the RO/DI. When I moved into my new house I noticed my RO/DI production capability went down dramatically, I found that my old house was running about 96psi, my new house around 80psi on the inlet side but only about 60psi after my pressure regulator.
I first tried opening up my regulator all the way, then found out that the reason for my house to have the regulator is that the showers have valves that are "on or off" (ie, no pressure control, just temperature control), and showers at 96psi hurt
So I dialed it back down to 60psi, and just tapped my RO/DI to before the regulator. Now that my area has grown the city has increased supply pressure back up to 96psi so I get about 80gpd out of my 100gpd unit.
Before summer comes I'm going to bypass my outside tap lines as well. 60psi isn't enough pressure to run two impulse sprinklers (the ones that go tsh-tsh-tsh-tsh-tsh!tsh!tsh!tsh!-tsh-tsh-tsh).
I can get by with one but as soon as turn on two they just sit there and stop tsh-tsh'ing.
Another factor to consider is temperature, and our water comes in pretty cold. There's not much you can do about this one though. Tapping hot water into the RO/DI supply is a bad idea because although it increases water production, it causes early membrane failure. So a lot more expensive in the long run.
But you can look into things like pressure booster pumps and permeate pumps to aid in increased production if you find "you need a little more".
Anyhow welcome to RO/DI