@Nga *************
I have the exact opposite experience based on people I actually know in that situation, who also speak fluent English. And those women watched several more women get rejected while they waited. They didn't see one single approval.
Common sense says the rejection rate for a single thai female wanting a tourist visa because of an American boyfriend is likely to be quite a bit higher than the 25% average. It was an automatic rejection for my now wife despite having two kids here, owning a business, land, house, etc. They flat out told her she needed to apply for the k1 fiance visa instead, despite the fact we had only recently met and any thoughts of marriage were still far out.