First thing is to (if possible) keep it centered on the garage door. This makes for a straight drive in without having to adjust for be centered on the lift. I have installed one post right up against a wall due to space requirements. I would stay at a minimum (if possible) 12' back from front wall MINIMUM as you did say SYMMETRIC not ASYMMETRIC. This allows for a tool box or bench or the ability to get a cherry picker in there for engine removal. I do not install PRO lift as it is not in my area. Lifts other than Rotary generally have a layout that is pretty accurate. If you doubt the measurements they provide, then stand the columns up, space them off what the book says and bring a car or truck between them to see if those measurements will meet your needs. keep in mind the side to side measurment will need to be kept as it directly affects the lift install BUT you can adjust the front to rear spec for your needs. You can also move the entire lift side to side a bit to suit your needs as well. Couple things to be mindful of. Overhead lights. Pressing a car or truck into them is bad. If lights are in the way even when vehicle is raised, you need to move them. Garage door. Make sure you can close the door with a vehicle on the lift especially trucks with plows, spreaders, and hitches sticking out. Options to consider if the power unit can be mounted on either side. Which is more useful to your needs? Try to avoid any cracks in floor by 6" from any anchor. Hope this helps!