7-14 psi turbo boost when engine compression brake engaged

Doesn't the variable geometry turbocharger on the ISL increase compressor exposure during retarder operation to raise intake manifold and cylinder pressures to increase retarder performance by increasing the power requirement needed to turn the engine?

Think of an air compressor "normally aspirated" by piston vacuum on the intake stroke vs one that is supplied with air compressed at 10 psi to start with - the second one takes more power to turn...