Decided to move pin 1 to a custom voltage divider & reset the 118k resistor to 35k.  The new voltage divider was a 10k pot + a 1k to keep it from shorting pin 1 to ground.  This allowed it to go from 5 - 16V without any trouble.  It also reduced the sag.  Now, 14V was enough to put the 12V maximum on the LEDs.  Left it there.  

The other problem was the cooling fan overspeeding at 14V & making a lot of noise.  It needed another 500R pot to slow down.  At least there wasn't an overvoltage protection, though short circuit protection was never tested.

The LEDs are rated for 5000 hours, so in 300 days they'll have to be torn down.  The square is the most efficient way to get maximum power to all of them with the least wiring.  It could use a string mockup to look neater.  Longer life & higher brightness could be done with $40 of derated strips.  The dollar store has 60W edison replacements for $1, but the modules run on 35V.  Making a square of these & just ordering a real power supply is another option.

Now you know how to get higher voltage from old computer supplies, for powering LIPO chargers, LED strips, & audio amplifiers.