Proper way to use LMDh systems?

You can test this how much fuel consumption changes between different modes, if you have Crew Chief you can bind a key or a button and he'll tell you how much fuel/lap you need as soon as he's got enough data.

The issue with high deploy is that while you might be saving some fuel you're draining the battery very quickly, you then have to re-charge it, which makes all the fuel saving before pointless as you're now burning more fuel. Once the battery is recharged again you want to save fuel again with high deploy etc.etc.

That's a lot of back and forth you don't want to do all the time while racing, it's not worth it. The best thing to do is find a balance, a mode that helps you use less fuel but also allows your battery to recuperate enough energy to never drain completely.
Find a balance, see how much fuel you need to complete your stint or the race and use that, as you'd normally do.

 

As if there was a mode called like that , huh ? Honestly, just use that mode and ignore the hybrid system entirely. AMS2 does not seem to simulate enough of the system to make it work properly, I am not even sure any brake bias is changed based on how much you recharge or on the battery level (unlike in LMU), I could not see any impact in my testing and telemetry in the past two weeks.

And in essence LMDh cars are just more on the passive side with it anyway. Maybe in quali... to carry even less fuel, but there is honestly little to win for the effort involved managing it. If you had deployment on a different axle or at different speed, like LMH cars do, then it would be worth figuring out where to deploy it to get that extra torque on the front axle (for example it can help stabilize the car through the Porsche esses, as you are basically turning your car into a pseudo AWD).