The plug stops against a step. No one here knows for sure if the step is drilled at the same depth in each block. So if the step is shallow (up from the bottom of the block) you may be trying to drive the plug deeper than that step.
Just look at the plug in the passage up into the block (that the oil pump feeds through the cap) and look at the side passage leading off to the side towards the filter location; that side passage will be obvious. If the plug is completely clear of that passage, then it is as far up as it needs to be. That plug just needs to be clear of the side passage so the oil can flow out to the filter. This is the right way to check this.... avoids any ambiguities of such measurements.
