To figure out how much glycine to supplement with, I used cronometer to determine my average daily glycine intake that corresponded to each homocysteine test, and then investigated the corresponding regression equation.
Although this correlation was just outside of statistical significance (r=-0.36, p=0.09), I can still use the corresponding regression as a rough estimate of how much daily glycine to take. That equation is:
Homocysteine = -1.36 *average daily glycine intake +15.4
I then aimed for a homocysteine target of 7.5 umol/L, which is close to my levels in youth, and based on the regression equation, I'd need about 6g of glycine/d to get there (assuming that correlation = causation, of course).
Based on cronometer's values, my daily average for glycine is ~4g/d, which means that I'd need to supplement with an extra 2g/day. We'll see how well this works (or not) with the next blood test, sometime in January!
For more info, see the corresponding video: