As I understand it, the main problem with placing the injectors far from the engine is that during wide open throttle fuel coats the walls of the manifold. Then, when you suddenly shut the throttle, this fuel evaporates causing an extremely rich mixture. This can cause a stumble, misfire, or even a backfire.

The other problem is that when you suddenly open the throttle, the pressure goes up immediately (as does the density) but it takes a while for the fuel to get the the other end of the manifold. This results in an overly lean mixture when you abruptly open the throttle. This can cause a stumble, or even a complete shut-down, of the engine.

If you always operate the throttle slowly, (like in an airplane) this is not an issue.

Bill Dube'