Hi,
The "Percentage" field there allows you to add an additional percentage fee based on the total amount of your cart.
So if the total amount of the products of the cart is 100€, a percentage of 10% would add 10€ to the UPS shipping fees.
If you use the "Weight approximation" and "Dimensions approximation" fields of your shipping method, you can increase the total weight/dimensions of the cart of 10% for example. The fees would then increase based on that. Although it's not exactly what you want, it's I think the closest available unless you start customizing the code of the UPS shipping plugin.