I've gotten different directions on that from different labs. You also have the filter if that's advisable and accessible.
Blackstone said middle of the drain, IIRC and another one said right away to capture the heaviest particles.
If you take the sample the same way every time it should eliminate the variable.
I understand you should take it when the oil is hot right after a good run. And take the sample after the oil has been flowing for a few seconds - if taking it from the drain plug. If you are drawing it via an extractor through the dipstick tube, you should draw the sample from a level about half way between the full and empty on the dipstick... you don't want to be taking the sample from the bottom of the oil sump.
I suppose that if you take it from the drain plug but don't want to do a full oil change, you can capture the drain oil in a clean catch pan and simply pour it back into the engine after filtering it through some cheesecloth or a fine mesh filter.