Long Arm vs Mid arm?

Does anyone know where to measure their caster angle from? Lower C or upper near ball joint? I'm getting 2 completely different reading left and right side. On top of me I am getting 5.5, but bottom 4.0. And right side I'm getting 5.8 on top and 5.5 bottom. I'm using an angle finder app on my phone.

Here's all you need in order to do the alignment yourself. Scroll down to post #4

: https://wayalife.com/showthread.php/3861-Basic-Do-it-Yourself-Jeep-JK-Wrangler-Front-End-Alignment
 
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