I stopped using drinking coffee in my enemas several years ago after I discoved organic enema coffee (Wilson's in my case.)
I found that enema-formulated coffee was easier to retain and produced superior results to that of drinking coffee. I found that drinkable coffee when used in an enema was too acidic for my colon.
My rule of thumb (other than for soapsuds solutions ) is that the enema solution is prepared at the same strength as I would if I were drinking it.