High power GPS mode?

Doesn't make much sense from the laws of physics point of view. Being a receiver only, how can you increase the power of receiving?

Power saving on electronic devices typically occurs by a chip switching on, doing its job, then powering down. The GPS chip already stays awake long enough to receive the full GPS signal. Staying awake for longer than it currently does won't improve GPS accuracy.

I agree with tmk2, as a receiver only, you can't increase the power.

Yup. There's nothing to be done to improve the signal-to-noise ratio by amplification; the receiver already continuously locks to the satellite signals; you could calculate the location more often than once a second, but that probably wouldn't fix any GPS issues you have, just give you more points. I can imagine some value in calculating often enough to model armswing and then cutting the output points to 1 Hz again.

Heat dissipation is another hard problem. The Fenix has to dissipate heat while being strapped to a heat source, your wrist, in potentially very hot air environments. Turning up the power also means activating parts of the chip that are otherwise not used and adding additional heat. From a manufacturing and marketing perspective, it is a waste of money to put in features and heat dissipation that aren't used most of the time. You are better off using all the features and throttling them on the rare occasions when heat becomes a problem.

Needed power in terms of performance is computing power, not the voltage level. GPS chip has specifications and power system gives that specified amount of power to it. More will make it hotter, less will switch it off. Actually it's already a 158 MHz chip but it's probably running in a lower frequency to lower consumption. Increasing frequency may help with more algorithms used to better filter singals and process but Garmin and MTK would have tried these solutions. Better antenna design can receive signal with higher gain and less false signals.

Mine is almost consuming %10 in an hour of biking activity with GPS ( + Glonass sometimes) on, cadence, tempe, HR sensors connected and some map and routing usage. Increasing consumption won't make it good for me. My Fenix 5X is really good with biking anyway. It's worse in running and lower speed walking but does its job. What I don't like is it records extreme max. speeds after pausing and resuming activities.

I agree. I let my fingers engage in typing before I let my brain get involved in what they were doing. :-) Teach me to have bright ideas whilst I'm half asleep in the morning.

I pretty much use it just for biking sis651 and it works great here. Well adding the speed sensor was a revelation in speed and distance accuracy. I still get around 5 percent use - rarely flip to maps unless I'm on a forest trail and get lost. I haven't seen extreme max speed for a while personally.