Artificial harmonics are a real knack. Try some of these;
Imagine pointing really hard like you are angry with someone - hold your i finger straight and firm like that.
Don't let the i finger depress the string at all.
Try the little finger to pluck esp if there's some nail on it.
Generally to balance in favour of the treble, slightly angle the hand lower on the treble side, higher on the bass side. And as well as that, see if you can get more follow-through with your finger than with your thumb.
Bear in mind that from where you are sitting the bass will always be more prominent, so recording yourself is the best way to know for sure how the balance is going.
Simon Ambridge Series 40 (2005)
Trevor Semple Series 88 (1992)
Louis Panormo (1838)
Alexander Batov Baroque Guitar (2013)