Its tapered, but about 2cm in one end and 5cm in the other. It's all the space there is :/ I might fill one of the middle sections later when i see how much space i need for cables, tubes etc...but i've seen machines with no EG in the saddle and they perform fine, so i think it'll be fine...it took almost all of the ringing out of the part...
However, if i was to start over, i might change the design of the saddle and allow for more space to fill with EG. E.g. instead of using a single 20mm piece of steel for each of the sides of the saddle. I could have used e.g. 8mm on the sides of each of the rail supports and then filled the void between them with EG... or not used steel at all and made it exclusively of EG;-) but....yeah, you learn something along the way :-)