Brake reservoir height

[AA-ron]

Hello Forum,
I recently had a comment on one of my build videos that my brake reservoir was mounted too low. I'm about 1.5 inches below the lip of the body (read as I could raise it 1.5" if need be). I mounted it just as described in the FFR build video but there was never any reference to exactly how high it should be. The nice gentleman that commented said that I'm running the risk of the reservoir syphoning fluid from the master cylinder. If I look at the relative position between the brake cylinder and reservoir, the cylinder sits exactly half way up the reservoir. I'm asking because it's a bit of a task to move it at this point, but I certainly will if need be.
Thoughts?

[egchewy79]

as long as the fluid in the reservoir is above the master cylinders, you should be fine. If you fill them too high, you might deal with some fluid puking out when you change your brake pads (when compressing the pistons). Just check fluid level periodically as the pads wear and you should be ok.

[MB750]

Siphoning only applies when the system is open to atmospheric pressure. Our reservoirs are sealed. That rubber gasket allows fluid to move down as the pads lose material, but they keep air out as well. Yes there's a tiny hole in the lid, but that is only to allow the gasket to expand as the level lowers.

Think about it... Let's say the brake fluid was being drawn from the master cylinder into the reservoir like that person suggested. Not only does that imply the brake pads and caliper pistons are retracting into the calipers, that also means the level in the reservoir is rising. What will happen to that air in the reservoir above the brake fluid but under the rubber gasket? Does that really sound physically possible based solely on the force of gravity?

Technically you could mount the reservoir anywhere in the car after everything is sealed. As the pads lose material the pistons will protrude out further which will suck more fluid from the reservoir, but it'll never go the other way unless you force the pistons into the calipers. Having it above the MC does help bleeding on initial fill though, unless you pressure fill the system.