This is not that hard… unless your neighbor has a high powered WIFI hub on the same frequencies as Smartthings zigbee. Its just a matter of $$ and placement.
Step 1: Use the key fob… If your phone is not reliable for presence then stop using it!
Step 2: Make sure your WIFI and Zigbee channels use separate frequencies.
IE my hub v2 is on zigbee channel 20 so my wifi in on channel 1 and the 2 devices are over 6ft away. Keeping your ST hub away from your WIFI access point/router is important.
Step 3: Zigbee mesh… to have a mesh you need 3 or more plug in zigbee devices. If you want it solid minimum of 3 plugin zigbee devices per 1500sq ft of your home. More is better.
IE ST hub and 2x smart outlets
Step 4: Have 1 or 2 plug in zigbee devices near the entrances/exits of your home. IE in your garage, the light switch for your front and back door.
If you can complete all 4 steps then you too can have reliable presences detection. My home is 1000 sq ft 2 story. It took 3 devices to make presence ok and 5 to make it bullet proof, but i also have A LOT of wifi inteference from every direction but up. I’d be willing to bet money that @bmad wether he/she knew it or not is in line with all 4 steps or has a lot of space between the neighbors and the home.