Glad you enjoyed it! Reducing understeer is a multifaceted endeavor. Right now, if you track enough (4+ days a year), I would get a set of Kosei K1 and some 245 or 255 tires. Same size all around. That should dial out some understeer and I bet you a single Kosei + a single good street tire will be cheaper than just a single runflat replacement. With all that pushing, you'll be chewing through your front runflats in no time.
In my mind, there is a hierarchy as to what you need to learn:
3) Corner Exit Speed
4) Corner Entry Speed
Entry speed is the LAST thing you should focus on. You can be a lot faster by focusing on corner exit because the extra x mph that you generate on corner exit will be carried down the whole ensuing straightaway. Maximizing corner entry speed gets you a few feet of driving faster. And it's really really hard to make super late braking consistent and you'll end up flubbing your turn in because the car is so unhappy from the 10.5/10ths braking.