Please check out the Problem and Solutions sections in the T629226: WinForms - Long text is cut off in DocumentManager tabs ticket.
We are going to improve this in the upcoming v18.1+. Our designer's favorite is #2, but we cannot implement it in a minor version due to a breaking change. BTW, option #1 shown in the screenshot below also looks fine. Take note of solution #3 as well - you can customize this behavior without writing any code.
Please let me know what option you prefer or if you are handling it differently. Thanks.
BTW, have you modernized your XAF WinForms apps using SVG icons and Light Style in v18.1? Click the screenshot below to see the new look & feel. Do you like it?