[American Constitutionalist]

" No, but it cuts down on wiring and complexity. Running anything thru the firewall (especially with 32/64/whatever connections is expensive and potentially troublesome. Having the powertrain controller mounted on the engine is a good design. "

That's all true and I don't doubt your word.

However ? there has to be some compromises if they want to have a car that runs on natural gas and have the room for it.
There are some modern cars that have the battery in the trunk now or in the floor boards.

[nascarnation]

My 90 Miata has the battery in trunk.

[Clay Moore]

I still don’t know where you are going to find all the room to get a spare tire in the engine compartment.

Are we going to raise the hood 8” or so?

Stretch the nose and drop it between the engine and firewall? Reverse tilt hood?

What about cooking the spare at 200*F for years till you need it?

I have seen the PCM’s behind the kick panel, under the dash and recessed into the firewall.

A late 80’s-early2K Ford PCM is about 10”x6”x2.” I doubt that the later ones have grown that much.