This chart allows you to determine the total training stress and intensity needed for your upcoming half ironman race. The higher your FTP, the faster you split and therefore higher your target intensity factor should be. You should start with the estimated bike split first, then review your hardest rides to make sure you have done rides of this training stress (TSS) and then look to find the corresponding intensity factor or (.IF).
Video data review - understanding the TSS pace chart in context with a race output - Tristar Athletes Peter Ekvall's data reviewed at the Maine 70.3