Try using the "Output polygon count" slider. This will reduce your model size but might affect the model quality. Here is more details on this feature https://makeprintable.com/features/optimization
Let me know how it goes.
I am not talking about file size. It exports 100 times bigger than what I upload - I simply want my model back at the same size. The whole point of using your service is to improve the quality of what I am doing, not make it rubbish. Which was what was happening in any case - with flat surfaces becoming bumpy and edges jagged. So I gave up and fixed it myself.
Customer support service by UserEcho