I don't understand your issue with component size.
For simple footprint components like C_Pad1 you would enter the actual pad size in that element.
The better solution would be to use an ADS component library. If you use the Murata library for example, you will find different size (0805, 0603, 0402 etc) in that library and can choose the physical size that fits your device. In the example below, I selected GRM02 series which has 0402 size.
View attachment 175784
View attachment 175783