I have a shower curtain up behind my birds' cages because they like to fling their fresh food everywhere. Unfortunately one side of the wall closest to Avery's cage is not covered, and every day I get the enjoyable task of cleaning up her wall art. Better than Lorikeet poops imho!
You can always work on finding out the amount your bird does consume, or at least fling, by weighing the food bowl before and after a day of it being there. Then you can work to keep just that amount in the bowl so there's less to waste. I feed my birds a pretty specific amount, and I find Avery only wastes pellets when she's frustrated that I haven't given her enough variety (I change pellet types, fixings, toppings, etc. very often) with her dry food. Of course if they finish everything, I always give more within reason. I just prefer not to free feed as I find my birds are more wasteful if I do.