Less slippage in Chelsea than engineer. The instep of engineers typically to allow entry also causes some heel slip. No big deal because they are not purpised for a lot of walking. Chelseas in my experience fit better for walking. A bit of slip but less than engineers.
You know that's a really good point about Engineer boots, that they're really not made to do a lot of walking in. Cowboy boots, Chelsea boots and chukkas, I can walk all day in them.