Help understanding some UT Flags, and advanced options

[asm86]

First of all sorry for the vague title, and if this gets long winded, hope it doesn't put anyone off replying.

Basically, I have recently been able to switch to fibre based broadband in my area with a well known British Company. I have a blisteringly fast top download speed of around 8.5MB/s which appears never to be throttled at any time (yet ) the bad thing is that the ISP appears to limit upload at all times, even off peak, to 125kB/s. Bad crack when it comes to staying on my few private trackers..or so I thought.

Anyway in the weeks since changing provider I have determined that the rate limit on upload transfers only occurs when a peer connects to me with 'U I' or 'U IE' flags. Just so you know I use the latest 3.1.3 build and Force Outgoing Encryption and Allow Incoming Legacy settings. I noticed, to my delight that if I stop such a seeding torrent, and then restart it, more often than not I reconnect to the peer downloading with just the 'U E' flags, this then allows the limit to be bypassed and I can hit my full 1.9MB/s upload. So, great I can stay on the private trackers!

Thing is it just gets a little silly at times when I have a lot of different torrents seeding, aswell as overnight periods where I cannot monitor torrents and do this stop/start procedure, and of course sometimes I lose peers to other seeds when I stop the torrent. There are some peers that I cannot get to connect without the 'I' flag, which seems to be the crux of it all. I was hoping that someone here could shed some light on this flag, or rather the reasons for peers connecting with it. I do on occasion get peers connect with just 'U E' to start with, which is great, are there any advanced settings that I could tweak to make this happen more?

I understand that unchecking Allow Incoming Legacy is one thing that could help, but I am reluctant as I may not then see many peers at all. Is there anything else that I could change in advanced options do you think? Also just out of curiosity does anyone want to hazard a guess as to the ISP's method of traffic management, I mean what does the 'I' flag being the key mean? I would love to understand more.

Probably bored you to death anyway if you didnt quit reading halfway through, I really would appreciate anyones input. Thank you.