I understand your hesitancy to perform more LST - your canopy has already outgrown the coverage of a single COB. But if you can get more light to the canopy, the additional LST will help greatly. If you already have the blurples, by all means add them. Can't comment on their quality as the Amazon listing has no technical specs, but any extra light should be helpful at this point. Two of those will use more watts than your single AutoCOB but I think you can most definitely use them.
The question is spacing, how / where to hang. If you can do a 45 degree hang at each side of the tent, with the lower edge (closest to the tent) a couple of inches beyond the outside edge of the plant, and 6" above the edge plant canopy, I think that will be most beneficial. Those are really small LED's - if the picture is accurate I counted 15 rows of 15 or 225 bulbs. At 34 watts-at-the-wall, that's only 0.15 watts per LED so their intensity will be minimal. You're going to need to get that close for them to help. Sidelighting? No, you need top lighting with the spread of that girl.
Keep your COB centered, but lower it to 12" as well. As big as your girl is getting you're going to need all the light intensity you can muster to keep her from fox tailing & ending up with loose fluffy buds. Don't worry about lowering the light, just do it by a couple of inches a day and watch for any light stress. The plant will harden quickly if it even needs any time to adjust (probably not).
@HemiSync has run his COB's as low as 5" from the canopy with absolutely no signs of stress whatsoever. I run my 325W actual at 14 - 16" and my plants love it. Just watch your ppm's - and remember, less light means less nutes can be absorbed. So if ppm's keep increasing, reduce your percentage of water to nutes.
An interesting thing with my plant, while I was in CA for six days my ppm's dropped significantly using early bloom formulation at 75%. But since I went to mid bloom, ppm's have started climbing (not too uncommon when veg is finished) so I've had to reduce my nute strength to 58% (7 gallons of nutes mixed into 12 gallons of water). And that's with six time the light you are using. So don't be afraid to go lower if the ppm's tell you that's what she wants.
I think your girl has had enough early bloom formula, and to discourage any more vertical growth I'd replace nutes with mid bloom but drop it to 50% (mix 2 gallons of nutes into 4 gallons water & save the remainder for top off).
If those buds don't start stacking up & filling in the internodal space after these changes, you have a big decision to face... loose buds or HPS. That plant in a 4X4 tent should flourish under a 400W bulb, ESPECIALLY if you have a cooltube reflector. If not, just ventilate the crap out of the tent & keep[ the light up at 15 - 16". She will fill out then.
Will check back, good luck & keep at it!