A friction shifted FD allows you to re-center the cage after a rear shift changes the angle ..

STI wont. you just live with it then.

Learn what the actual Gear ratios are

once you get to the edge of the cluster in one chainring the Ratio overlap is probably where you are and
double shift to a similar ratio in the other Chainring

go to a gear calculator input the tooth counts and wheel size, Print up a chart , tape it on your bike.