They're not mapped to have a spike, it happens due to slow responding VNT. Now that i have my laptop on i can look at a standard map:
Standard map requests 1.4 bar at 2000 rpm, rising to 1.5 bar at 2500 rpm, holding that request until 3750rpm where it will start to tail off to 1.1 bar by 4700rpm. So anything more than 22psi is a spike/overboost