If you have .05ml deadspace, and you fill to 0.2ml, you really filled to 0.25ml, but only 0.2mL of the oil can be pushed back out.
If you use insulin syringes, there’s even less dead space, but as it’s already been said - it’s irrelevant.
If you wanted way more information than you’ll ever need on the subject…
P.S if you overthink a lot, you may find that keeping lower estrogen levels puts this on pause. At least, it has done so for me anyways.