It's easy to have the boot open automatically and fully on XF.
I replaced the small rubber grommet that the spring pushes against on the boot with a slightly thicker one. You have to drill a small hole and use a self tapper. Be careful drilling, don't go through the outer boot !!
Then £18 worth of new gas struts from eBay.
job done in 30 mins and now it springs open fully every time.