Looks great! Don't sweat it.
Just a little lockout I think.
If you're supplementing the same amount of nutrient to the smaller plant, as the larger one, then I'd say it's good indication to cut it back a little.
Be sure to run a little waste each watering too. Smaller plants often don't drink as much water either. So bare it in mind. It mightn't need water / nutrient as often as the larger one.
Larger plant's super healthy looking to me. Really nice and green! Great healthy colour.
Notice though the same symptoms are starting to show, only ever so slightly.
I think it's good indication to just lower your total EC a little. I'd expect the larger plant to be worse off than the smaller if the reverse / underfeeding / deficiency was true.
Have you been following their feed chart / feed amounts?
If not, then please say. I'm working my own assumption from your provided information, that you are.
Maybe a plain watering once, next time they're thirsty, instead of nutrient. Up to you, honestly your own call.
Nice plants, looking swell.