Conventional thinking on exhaust manifolds or any inefficiency in the exhaust system is to open the exhaust valve earlier so that the supersonic "blowdown" lasts a bit longer on the exhaust stroke.

It never made sense to me to open the exhaust valve early because it seemed this wasted the still expanding gases pushing down on the piston during the power stroke.

I finally understood it when it was explained that if you dont open the exhaust valve when there is still quite a bit of pressure, you dont get a short period when the gases accelerate past the speed of sound and create a sonic boom like a jet fighter. This sonic boom has a high pressure wave at its front, but also a strong suction wave just after. The cam designer wants this suction wave to pull up the piston on the exhaust stroke, which reduces the power the other cylinders would have to apply to raise the piston.

Does residual gas in the combustion chamber increase the chance that detonation will occur with a high compression ratio?

Mazda seems to think so
on their new 13 to 1 compression ratio
Skyactiv line of engines.

In their press release they spend time explaining that their Tri-Y exhaust manifold was necessary to get the compression ratio high without detonation on 87 AKI gas. At full throttle they claim that the heat brought in with the residual exhaust gas is a bad actor that had to be reduced.

If your 200 psi cranking pressure is causing detonation,
in addition to cam changes
consider grinding a few more CC's of combustion chamber volume on the exhaust valve side