Why Dominion fleets counted with the Royal Navy

Why were Dominion navies included with the Royal Navy in treaty limits?

Otherwise Britain could evade its limit by handing ships to Dominion navies while retaining their effective strength within the imperial system.

Including Dominion fleets prevented Britain from expanding its effective navy through transfers. If Canadian, Australian, and other Dominion ships sat outside Britain's allowance, the Royal Navy could enlarge its effective fleet simply by transferring hulls to them. Those vessels could remain available to a combined imperial command even under separate national ownership. Counting the wider imperial naval system together prevented those transfers from defeating the treaty's intended balance.