Which wire in this configuration is line and subsequently which ones are load?

[![rough wiring diagram](https://i.stack.imgur.com/mwgB7.jpg)](https://i.stack.imgur.com/mwgB7.jpg)

**Legend**: B1-B6 are 6 black wires.

**Not shown**: each switch has ground wiring as well. Left them out for simplicity. There is also a clump or neutral white wires in the back of the box with a wire nut around them all.

**Context:**
Two light switches where the left switch controls lanterns next to a front door and the right switch controls a light post. They are independent. Turning either off doesn't affect the power to the other.

**Background:**
I’m wiring in a smart switch Caseta by Lutron and it has a black line in and red load out. I want to swap the right switch with this and need to know which of the existing two blacks is line in vs load out to the light.

**Commentary:**

The electrician used a red wire nut, not sure if that was intended to indicate something about all of those black wires.

I was a bit confused by this configuration because my assumption is that B1 is line, and through the left switch it caries power up to the red-capped pigtail and that feeds power to the right switch via B5. However when left switch is off, right switch still works.

My assumption is B1 is line, B3 and B4 go to each of the lanterns, and B6 goes to the pole. B2 and B5 join the switches.