I know, that bloody sign... unfortunately I can't remove it in the editor, so either I have to raise the entire track (lots of effort, won't do this) or reduce the width of the back straight (difficult because this is also where the pit entry is, and it would need like 4-5m to clear that sign, so I won't do this either).
Moving T1 further outside isn't an option. The only approach I could think of is introducing a "dip" at the end of T1, so T1 goes downhill and the back straight goes uphill. Not sure if that's any easier to do, but it might work.
Currently the car sits at ~2.6m with about 0.75m of clearance. A typical car would need about 0.5m of additional clearance, so that might be possible.