Originally Posted by
ckindt
Yes, if you have an open system with a bladder separating the air from the fluid.
No, if you have a closed system with no bladder.
There's air in the reservoir by design; it's why Shimano tells you not to invert the bike - it might work its way between the lever and caliper and cause sponginess. You wouldn't need to open the system up to push in the pistons and gain another half mm of gap.
Again, there's no rub unless standing - that should tell you that it's not that far off. Recommending that the OP open up the system to remove fluid when there are dozen other exceptionally common explanations is pretty... yeah, not prudent.