Mileage Reimbursement

I found an old thread (2014) related to this, but not as detailed as I a looking for. We had a policy in place for years that when traveling to a temporary work location mileage reimbursement could be submitted from the location that was closest (from the normal assigned office location or home). Recently the policy changed to mileage from home to the temporary location has to subtract the normal commuting miles. For the most part, this seemed fair and was met with little resistance. Then it was clarified/added to "The method of commuting to work does not change the number of miles that are incurred to commute from your home to the office." The organization has many people who take public transit. The normal commuting expenses that they have is not reflective of the actual miles from their home to their work. Now we have employees who commute 20-plus miles a day to work, but commuting miles at their expense are often 3 or less. Looking at this document (https://www.irs.gov/pub/irs-drop/rr-99-7.pdf) Under Rev. Rul. 94-47, a taxpayer generally may not deduct daily transportation expenses incurred in going between the taxpayer’s residence and a work location. A taxpayer, however, may deduct daily transportation expenses incurred in going between the taxpayer’s residence and a temporary work location outside the metropolitan area where the taxpayer lives and normally works. In addition, Rev. Rul. 94-47 clarifies Rev. Rul. 90-23 to provide that a taxpayer must have at least one regular place of business located “away from the taxpayer’s residence” in order to deduct daily transportation expenses incurred in going between the taxpayer’s residence and a temporary work location in the same trade or business, regardless of the distance. Does reimbursement according to the IRS mean all miles or miles at their expense? Does it matter how the miles are traveled to the normal assigned location v. the temporary location?