If you have 100 parcels you'll have the last 5 be reinjected. But... with 1000 particles you'll have 905 reinjected. So a random number function may be better.Â
Now, for the actual return part. If a parcel hits the outlet does it leave the domain before the UDF triggers? If you put a surface at a few cells into the domain (porous jump are really useful for this) does behaviour change?
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