As a rule I find the Epson won't start a print if it thinks there is not enough ink to finish it, or I assume that's why because it won't print until I've changed the offending cartridge. So how does it know?
Interesting. As a rule I've never seen an Epson refuse to print a print because it thinks it doesn't have enough ink, only refuse to clean because it doesn't think it has enough ink. However I don't use the small cartridge 2880. The printer will normally stop and ask for new ink when it runs out, which is often after the indicator has been on 0% for some time. On the large printers, as much as 10% of the ink still remains, enough for a large number of prints, when the indicator says it is empty.
As far as putting less ink in the cartridges I would be surprised. Ink consumption is extremely variable based on print subject matter, paper choices and print settings. Epson provides pretty detailed ink consumption expectations ...
"Ink Yield Information:
Epson provides ink cartridge yields based on the ISO / IEC 24711 and 24712 standard for inkjet products, which excludes the first installed cartridges.
Matte Black (T096820): About 495 pages
Light Black (T096720): About 6,210 pages
Light Light Black (T096920): About 6,065 pages
Cyan, Vivid Magenta, Yellow, Light Cyan, and Vivid Light Magenta (T096220, T096320, T096420, T096520, T096620): About 940 pages per color"