To remove the 3rd layer in the Technical Proposal, I commented out in PixelTechnicalProposal2014.cfg the lines :

 // Layer 3 {
 //   radiusMode fixed
 //  placeRadiusHint 109
 // }

The original resolution is:

pt 1000 Real 2.30948 Ideal 0.53651 Loss 4.3

d 1000 Real 0.00601 Ideal 0.00241 Loss 2.5

z0 1000 Real 0.00696 Ideal 0.00273 Loss 2.5

These changed into:

pt 1000 Real 2.14395 Ideal 0.75964 Loss 2.8

d 1000 Real 0.00606 Ideal 0.00305 Loss 2.0

z0 1000 Real 0.00698 Ideal 0.00275 Loss 2.5

To move the layers the parameter to change is the placeRadiusHint. Moving the layers closer to the interaction point leads to a degradation of the pt resolution and to a slight improvement of the impact parameter resolution.

With 4 layers: (2.9, 5.8, 9.9, 14.0) performance are generally worse.