Why is mobile IP detection still so flaky for my tool?

my 'what is my ip address' tool is still throwing a wobbly, but now it's more subtle. it's not failing outright, which is progress i guess? but it's giving wildly inaccurate geolocation accuracy for mobile users. like, someone in LA gets 'Ashburn, VA' and their 'ISP' is some generic carrier proxy. it's infuriating 'cause the IP itself is often a valid one, just not *their* actual one or close to their location.

i've tried a bunch of stuff since then:

• switched IP lookup APIs – bounced from ipify to ip-api.com, then even tried a couple others. thought maybe one was just better for mobile.
• implemented reverse proxy headers parsing (X-Forwarded-For, X-Real-IP, etc.) way more robustly. made sure my server was logging everything.
• tested extensively on different mobile carriers (verizon, at&t, t-mobile) and various wi-fi networks. borrowed friends' phones, even my grandma's flip phone (just kidding... mostly).
• checked server-side logs for discrepancies in request headers vs. what the API was returning.

here's what i often see in my logs or from the API response for a mobile user who i know is in, say, miami:

// Example of an incorrect API response for a mobile user
{
  "ip": "192.0.2.1", // Often a proxy or carrier IP
  "country": "USA",
  "city": "Ashburn", // Not the user's actual city
  "isp": "Verizon Wireless",
  "latitude": 39.0438,
  "longitude": -77.4874
}

so, what's the secret sauce here? are there any advanced strategies i'm missing for truly reliable mobile ip detection and good geolocation accuracy? is there a specific header or a combination of APIs that just *works* for mobile? how do the big boys like google or netflix get such accurate locations even for mobile users?

this is really impacting the user experience for some of my features, so any expert advice would be seriously appreciated. i'm all ears!