Ok so you have them in one corner of the 12x12 room.... If you can stand on the opposite corner of the room and light is illuminating the corner in which you are standing, from your plant lights, you are losing lumens....

18"-24" from a 1000w lamp is the most effective range for a 1000watter.... Anything closer and the foliage will bleach from light intensity.... So YES, I do believe your 90w being 18" away is still ineffective....

Plus your plants told me everything I needed to know.... Your two LARGE plants are stretching like crazy and are just tall not large.... At least that's the way they look in the first two pics....

Will be waiting to see your full grow space....

You are right about the insufficient lighting not being the cause of the brown tips though....

CGI::::::