LibertyLobbyist

I recently reached PPro and I'm trying to better understand the upgrade system.

I have a RT from TUS to CMH through DFW, departs tomorrow (Monday) return Wednesday. I was upgraded on the DFW - CMH leg an hour after I booked the flight on Friday the 14th (so was in the 72 hour window). I was not upgraded on the TUS - DFW leg but there were only 2 FC seats showing open on that flight, so they sold or went to higher status folks.

Then I got an email this AM that I was upgraded on the return leg CMH-DFW but nothing yet on DFW-TUS. There's 5 FC seats showing open on the app when I look at that flight as a new booking. All this is to ask 3 questions:

1) The obvious question is why isn't it upgrading that leg as soon as it hits the 72 hour window with 5 open seats? I assume if there's one or two they want to sell them so wait till the last minute to upgrade status folks. But why no UG with 5 open seats?

2) I assume the system waits for each leg to reach the 72 hour mark, is that correct? So if my first leg hits 72 hours that doesn't mean the 2nd leg is eligible until it reaches the 72 hour mark for that flight.

3) I guess I'd also like to know if this changes when I reach EP or are UGs confirmed at the 100 hour mark as long as there are FC seats open?

I'm just trying to figure it out. I fly for business and book last minute a lot, I often have flexibility to to try to book flights with more seats open in 1st to increase chances of upgrades. Any other tips for increasing odds of UGs?