Depth of water in the bowl is controlled by toilet design and height of
the built-in trap. While you might be able to reduce the amount of water
per flush with the old bricks in the tank trick (to still give high enough
level for flush pressure, without as much volume). But reducing amount of
water in the bowl requires a different toilet.
If both toilets are the same kind, it is possible that the one with the
lower level has some sort of crack or leak in its trap, or the little hose
off the the float control is not connected the same.
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