Ball mount rise, or drop, is determined by inserting the ball mount into the hitch on your vehicle and measuring from the top of the hitch opening to the top of the ball mount platform. I added a photo showing how the rise and length would be measured on the Draw-Tite Ball Mount # 3594.
We also have an informational article that explains how to choose the correct ball mount for your application. All Class I and Class II trailer hitches are tested and rated with the specific ball mount... view full answer...
What you will have to do is measure from the top of your hitch opening up 4 inches and then from that point measure down to the ground to know where the platform will end up.
We haven't had the chance to get that measurement on 1998 Buick Regal yet. view full answer...
We do have a solution for you but unfortunately trunk mount bike racks, like the Thule OutWay # TH45JV that you referenced, only have a weight capacity of 33 lbs per bike. Any trunk mount bike rack that has a higher capacity will not be much higher than that, maybe 35 pounds.
If you have an e-Bike then you really need to go with a hitch mount bike rack as your bike probably weighs closer to 50 lbs. For your 2012 Buick Regal I recommend installing the Draw-Tite # 36538 which is a Class... view full answer...