I like that tomnik had some evidence due to the dynamic timing device to support what he said.
To prove that lower injector opening pressure yields more fuel injected I would like to see the IP on a test stand and the fuel quantity measured at the high pressure (maybe about 10 test runs at that pressure) then have the same injector adjusted to a lower pressure and the IP run again (for another 10 test runs) and fuel quantity measured again and compared to the first measurement.
The variables could be the fuel that leaks by the injector pintel and the IP elements (plungers and barrels) which is needed for lubrication. A higher injector opening pressure might cause more "leak by" in those areas.
Is this enough to justify lowering the injector opening pressure just to get that tiny bit of fuel more and loose the benefits of the higher opening pressure?

The injector hard lines swell under pressure so some fuel is lost due to some of the fuel quantity being still in the injector hard line when the nozzle closes. So higher injector opening pressure = slight uninjected fuel loss.
I do not think so. As soon as the nozzle opens the pressure is relieved on the injector hard lines witch would return to its unexpanded size because the hard line is not a springy as the nozzle spring it will return to its shape fast. Try it with your garden hose and a nozzle with a shutoff.
When shutoff the hose is swollen; when the nozzle is opened the swelling goes away.

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84 300D, 82 Volvo 244Gl Diesel