Wirelessly posted (iPhone 3G: Mozilla/5.0 (iPhone; CPU iPhone OS 8_1_3 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Version/8.0 Mobile/12B466 Safari/600.1.4)
Whilst I welcome the explanation, I'm not convinced by the argument for siting the measurement point pre-security.
For one, it creates a clear incentive to allocate resource to primary screening security. As despite was was said, it's very easy for primary security to continue to process quickly whilst a handful of secondary bag searches (some of which are random so "no fault" by the passenger) mean a wait of 20+ mins with no impact on the pre-security queue.
The secondary search queue will only impact the pre-security wait when the secondary trays back up to the x-Ray exit.