I just did two applications, a week apart. My curl pattern didn't decrease at all, but I'm sure I haven't done enough to see if it will or not. My hair was a lot curlier after using half henna and half amla. I wouldn't recommend the 1:1 ratio though, it had a bit of a drying effect. I toned it down on the next application to a 2:1 ratio and my hair feels amazing!

I think there may just be anecdotal evidence of amla helping keep your curl pattern when using henna.

I was wondering too - how the heck do you apply just to your roots? Will there be an overlap that is darker and look weird?
2c-3a - med-coarse - normal-high porosity - high density

NP/LP: CJ Daily Fix, KMF Whenever / Giovanni TTTT
RO/LI: Aussie Moist, CJ Argan & Olive Oil, Hask Keratin Protein
DC/PROTEIN: KC Stellar Strands / CNPF
STYLER: CJ Curl Queen
COLOR: henna, amla & indigo
: glycerin in high/low dews, polyquat-10 & 11, parabens