Direction of Pressure Relief Valve

Was looking through the manual for our recently installed, and still uninspected, hot water heating system

Everything in it, the illustrations for installing the boiler and the written directions, indicate the pressure relief valve should be mounted upright. The manual reads: "3. Orient the manifold with the relief valve on top."

Ours is mounted into a T from the side, in such a way that it's drain is aimed directly down. Does it matter?

I thought I'd ask this stupid question only because it's an important safety device.

They can be mounted horizontally but they need to be mounted in the top 6" of the boiler water jacket.

I don't know if it's 6" from the top of the water jacket, it's hard to tell where that is with a well insulated cabinet. On the Burnham ES2, the gauge is supposed to be installed at the height of the supply outlet, upright, and the supply outlet is about 14" down from the top of the cabinet.

Ours is installed at that the same level as the supply outlet, but is horizontal instead of the illustrated vertical. Safe way to do it?

Again, thanks for answering such a petty question - but then again it's not so petty if the valve is not doing it's function.

It should be fine as long as it's in the top of the boiler

Turns out it's not approved for horizontal install, only upright.

It was not tested in multiple positions, and the sideways pressure fluid dynamics exerted on the spring are supposedly different than if it was upright. Manufacturer said upright, so it will be.