if you know the block geometry then set snap to off as you know the point you want to join to relative to the insertion point of the block, it becomes more complex with X & Y scale and of course rotation adds even more complication. eg block creation insert 0,0 point is 1,1, in dwg inserted at 23,24 so end of line is 24,25.
If it varies say block is a square then ask "which corner" to connect line to correct corner.