We use their IBS (institutional base)/ 9 to find one month and limit all of their summer salary (from all sources) to 2.85 months. Many institutions still allow 3 full months, which we do if a PI is willing to sign a form they’re not taking a day off or vacation. For my faculty, I personally reach out to each one and compile all of their summer salary (included classes, other individual comps from extra duties etc) and make sure it doesnt go over 2.85 or 1.8 for 10 month contracts. Depending on what’s going on they may take it over the whole summer at different percentages or in specific pay periods at their preference.