Spitfire IIa prop pitch

[wallydog69]

I was curious about how the Boost Gauge worked in relation to the changing the prop pitch in the Spitfire IIa. I've noticed that when increasing/decreasing my RPM setting that my manifold pressure will adjust accordingly... is this correct operation? I'm not changing my throttle at all. I'm typically used to seeing the MP stay consistent with the throttle applied so this is a bit confusing for me. Any response greatly appreciated.