Most MAP sensors don't sense boost; they have to be designed for the particular range of plus and minus pressures. The kind that sense boost are more expensive. So the question is valid -- did your system come from a turbo car?

Rising-rate regulators are just one way of fuel management. It depends on how the system is designed. In 99 Ford switched from rising-rate to non-rising rate, and that's on the non-turbo 4.6 liter. Interesting question about "undersized" injectors. The factories use rising rate, but aren't driving the injectors at pressures higher than the spec'd pressure.