Sourdough starter troubleshoot

Hello all!

First time posting to TFL, this site has been so helpful to me already!! 

I have a sourdough starter and I am wondering if anyone can help me determine if 1)my starter is healthy/active and 2)if not, how to boost it? I have a 50/50 BF/WW starter at 100% hydration based on the Tartine basic starter recipe. I have had it and maintained it for about 5 years. Sometimes I do put it in the fridge if I don't plan to bake for awhile, but recently my feeding schedule is roughly every 12 hours, and I feed in ratios depending on its growth over the past 12 hours. For example, if my starter has already begun to fall at 12 hours, I would feed at a higher ratio than I did the time before, so instead of 1:4:4 I would feed 1:5:5 or 1:6:6. I use small quantities like 5 gm of seed starter per FullProof Baking's recommendations.

I almost always feed at least a ratio of 1:4:4 or higher and can get a 2x rise by the 12 hour mark. I store it inside the microwave so its a little warmer than it would be out on the counter. I know that Trevor Wilson defines a healthy starter as 2x growth at 8 hours with 1:2:2 feed, and I feel like I get this. However, I have never quite gotten that 3x growth that I see some people getting. How can I boost my starter to get there? Even with feeding every 12 hours consistently for many weeks I typically can only get 2.5x rise at most.

Since starter health is so important to the final bake I am really wanting to see it go that extra mile! Any feedback or tips are so appreciated :)