On my 2011 Escape; then on my 2015 Edge, and now, on my 2018 Explorer, I've always put my floorjacks in the designated under-rail slots behind and ahead of the wheels as needed (as noted above), without any problem with a "bending" of the rails. They seem to be pretty solid and strong at their designated lift points. However, I also just recently found a hard-rubber "hockey puck" style of adapter on eBay, similar to the unit shown in the previous post, and I'll be trying those out on my next oil change, just to see how it works out.
When I change my oil, I put floor jacks under the railings just behind the front wheels, then jack it up, leaving the floor jacks in place... but also placing a sturdy jack stand underneath the vehicle for backup safety reasons, just underneath the rear edge of the A-frames. This still leaves me enough room to fit my large oil-catching pan underneath, to do what I need to do.