I am installing a circular window in a building with metal barn siding.  It is a board and batten pattern.  My question is how do I flash the lower half of the window?
I get that the top half will be flashed with a J-flashing section,  the back of the J-section will get attached to the sheathing and will be covered with flashing tape and the metal siding will slip into the channel.  the bottom half has me stumped.  I see water being caught in the top j-channel,  running down the sides and then when it reaches the midpoint spilling out onto the sheathing.  I will be installing ice and water on the sheathing and a rain-screen so water that flows off the upper portion of the j-channel will theoretically not damage anything.  But still I feel uneasy about water getting back behind the siding. Any ideas anyone?