would have to be hubcentric, as its the centre that takes the load of the wheel, bolts just keep in place, there is a big difference handling wise between using spacers to increasing track, and using spaces to correct track due to different ET on wheels
Having given my puma on standard suspension a proper hammering on track, it may look a a bit 'wallowy' but is very controllable and feels well suited to car, personally, the biggest handling problem on the puma is the standard seats, as lack of support, sculpture, and designed more for an old dear to drive to town once a week, they are a must do, before even thinking of going anywhere with suspension, if you are going for handing rather than just looks.
My feeling is anything that stiffens up and looses standard characteristics, moves away from what the car was designed to drive like, ford spend thousands, and have specialist engineers to set the suspension, obviously within budgets and parts bin robbing, but its often hard without a lot of specialist knowledge and expensive experimentation, to improve on stock.
just my ramblings, but having seen the pain of people who have bought and then binned fairly fancy set ups, and driven cars with various mods that make car look and sound better, but at the expense of the driving experience.
Really you need to find some cheap 2nd hand 15mm spacers, book a trackday, fit an in car camera and you can then do side by side direct comparisons.