ok guys, please, before you all have a go at me, sit down for a minute, and give some thought to the suspension on your leon.
At the FRONT end, you have a fixed lower wishbone, with a hub attached via a ball joint, then a Macpherson strut type arrangement. The front upright is attached to the hub VERY rigidly, and the only point of contact to stop the hub flapping around, is the top of the upright.
In this kind of setup, any movement at the top of the strut, will result in a change of either camber or castor, or both, as moving the strut, directly effects the hub and wheel geometry.
Adding a brace here and stopping chassis flex will reduce the amount that the front geometry can change during body flex, so the results MIGHT be noticable.
At the back of the car, you have a fixed beam axle. This also has flex along it's length, to give a degree of independance to the rear wheels, but aside from the flexy centre, the trailling arm sections of the beam are fairly rigid, and the wheel is mounted via a stub axle to the rear beam.
The rear beam mounts to the chassis, at a VERY strong reinforced point, at floorpan /rear squab level, some 18'' forward of the rear wheel centre. The rear springs are also mounted to the beams trailling arms, and compress against a bulky chassis rail, just behind the beam mounts.
The rear wheel geometry is fixed by the rigidity of the beam, and cannot be altered without camber shims.
The rear shock absorbers on the leon, are mounted via a highyl flexible rubber bush, at the back of the trailling arm section of the beam. then into the wheel arch via an alloy top mount and 2 bolts.
These rear shocks take load in compression ONLY, and take no lateral load what so ever.
As a result, bracing the top of the wheel arches, on a leon, will make NO difference what so ever.
if you don't believe me, think for a second about what you're bracing. it's the top of the shocks right?
Now, if you REALLY don't believe me, unbolt a shock, and grab hold of the top, and wobble it around as violently as you can manage.
You'll notice, that the rear wheel geo does not, and can not, change as a result of moving the upper shock mount on the back. Even if you ran no shocks at all, rear wheel geo wouldn't change, at all.
For this reason, surely, you must agree that bracing the top of the shocks cannot make any difference what so ever?