How to bleach roots?

I bleach bath my roots since my natural colour is blonde. I mix the bleach and get my sister to apply it to my head since I can't do the back of my head myself. I use a tint brush to apply the bleach to my roots only and wrap my head up in cling film until it's done.

I have resistant dark ash blonde hair that grows about an inch a month up top and about a half inch a month on the bottom layers. I try to do my roots every 5 weeks so I don't get any banding. I use matrix Light Master, a very fast, high lifting bleach, and I make a bleach bath with it. I use 2 oz 30 vol, 2 oz shampoo then add the bleach powder until it's like a thin yogurt like consistency and apply it to hair that's been slathered in coconut oil from that morning and the night before + hasn't been washed in at least a week. I do the 'hot cross bun' sectioning, starting with the back sections and do the 2 front ones last. It takes 10 minutes to apply, then I cap it and let it set for another 15 minutes and I'm pale yellow