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What he appears to want is to park, turn off the car, exit and walk away, and for the car to lock itself when he's out of range, without having to use the fob. That's how I understand it anyway.
I'll just lock it by touching the indent on the handle and watch my driver side mirror fold. I'll be standing merely a few inches away from the door handle anyway after existing the car. I won't even have to look back to see if the mirror folded. If I can remember to take off my seatbelt before trying to get out of the car I can certainly remember to touch the door handle - then I'll save the need to look from afar to see if the mirrors actually folded, or not. The feature the OP wants in my opinion is totally and completely worthless...and Lexus no doubt thinks so too!
Simple solution as stated by @bclexus - get in the habit of either locking via key fob OR touching the mirror to lock the car - for me the folded mirrors is the key to confirming the car is LOCKED - not that difficult.