Honestly it's really luck. I've read where millermatic 211's have arrived beat to crap. I use to do a lot of ebaying a couple years back. I sent stuff triple wrapped and double boxed and it would still get damaged. I've sent stuff with absolutely no packing material and it arrived just fine. The current foam is adequate and has some give to absorb a fall, but considering the weight of a welder it can only take so much.
Have you ever tried filed an insurance claim with FedEx? I've been through that twice and have never been refunded even though I purchased additional insurance.
The larger the box the more it cost to ship! When fuel prices started going up several years ago UPS and Fedex started using some formula for size and weight.