Yeah I sprayed with neem as well on my plants at week 2 or 3 of flower on my last run and they don't seem to smoke any different. I wouldn't want to spray any later than that though just because everyone says not to.. although a few people have told no to they sprayed later into flower and didn't notice any bad taste..
My buddy I guess has sprayed some old school stuff they use to use back in the day, 3 times and he says it seems to kill them but then they come right back so he's thinking they're coming from/hiding out in the soil. I have a few different things we can try. Probably will start out with the soapy water and sprinkle some DE onto the soil.
I've been told as far as the ratio goes that you only need a couple drops, just enough so that the bottle isn't filled with large bubbles but if that worked for you and didn't seem to harm your plants then that's all that matters. I've only ever used neem oil but I'm pretty new, grew outside a couple times about 7 to 8 years ago when I was just a teen and now just finished up my first indoor grow..
I'll let you know our results though, shouldn't be too bad I don't think