1. There is an option in the chart options section to adjust the whole header height(in px)
After that set height of each header level in the timeline section(in percentage)
if top-level takes 30 %,mid-level takes 30% then automatically for the last level it will be calculated as 40%.
2. In the Reading view that pencil icon won’t be visible. you can off the summary table then the table icon won’t be visible.