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[MyISPHatesENWorld]

The following add 1 square to the distance of a push::
Gauntlets of the Ram (Lvl8)
Controlling Weapon (Lvl8)
Rushing Cleats(Lvl7)

So Tide of Iron plus any of the items above also gets you an at-will knock prone. It seems pretty likely they were aware of at least one if not all of those items... Hard to imagine it isn't intended. At Paragon, you can pick up Spear Push and do it without an item.