According to some charts* made by RUNWME (with a one putt stat of 65.62%, score av. 57.24 and earnings of $7,135.45) he/she shows different charts for a couple of different putters all on different green speeds.
If I'm not mistaken, all the charts are showing that 50% power is half of 100%. These are all on flat greens and 'ideal conditions' I guess, but there is a likely chance that the game programming has changed. It looks like he/she isn't playing recently.
Nike and Daytona putter charts
I don't reference the charts personally, as I have similar calculations already, and we all have our own methods, etc.
For example, my experience tells me a short putt approx. under 15 feet needs more power maybe 'for inertia' to get moving , while a really long putt has 'momentum' so I shave off a percentage.
This concurs w/ the idea that the power is not linear, generally, but that's mostly due to the inertia observation above and the almost 'exponential' affects of wind, etc. I still consider 50% of my 60 foot increment to be approx. 30 feet.
(e.g. GENERAL EXAMPLE a putt of 8 feet I'll hit at 9 feet of power, and the same green speed if it was 100 feet I'd hit with 92 feet of power, see what I mean?)
Results will vary but it's just something to observe.
If it doesn't help - disregard it.
If it helps give you a starting point - look into it.
*
Nike and Daytona putter charts