Ready for Transplant to Hydrocorn?

@The8thChevron - thanks for the reply. These are Barneys Farm PhotoPeriods. Roots are starting to pop out of the Root It Plugs on them all so will transplant tomorrow night to save root issues. May I ask some advice. As 2 are pretty much 3.5-4" height and the other 2 I am keeping are around 1.5" height, I would like to bury the two taller under the corn a bit to keep it all even. Have you ever done this? If so, do you need rooting gel to make the stems pop roots or should they usually do it when not exposed to light? 1st time solo growing and using hydro rather than the soil I was shown a few years back so relearning and and classing myself as a 1st time grower due to it! The bottom left one is getting its baby leaves yellowing and drying out so thinking its defs strong enough to hold up to lower end of the veg feed, was just worried about the others. Any advice is greatly appreciated and thanks again for your input.

As an add on to the question, bottom right was stunted due to me thinking it was a dead seed - got binned in a bag while still in plug - 12hours later it had sprouted so got saved (I shall call it Lazarus/Binderella - think its a purple punch but could be cookies Kush)...its as stout AF though so staying. Bottom left is the 1st to sprout (Should be 12 days now - it got a stretch as I used a warm 27W CFL as 1st light and was in higher humidity so it took a stretch). Top left will probs be a donator to someone as a freebie as I only have room for 4 (Using a Wilma 4 pot). Top mid and Top right will be keepers. For scale, top mid leaf width is 1.25" per leaf.