I generally dehydrate kangaroo, at about 3% fat. No problems. There will always be SOME fat, but less is better. I have to say I have NEVER washed my meat after cooking. I feel like this would take a lot of the flavour with it. However I've never used 10% either.
I generally work out amount of water needed by weight. Weigh your mince before dehydrating, and again after you're finished. This works out how much water you have taken out. I write this on the portion, to know how much to add back.