Well, as I've said earlier, in my situation with that particular woman, being the same height as the 5'11'' was one of my disqualifiers for entering an LTR with her.
The threshold is higher for LTR than it is for a fling
Flings are mainly about sexual impulses, while LTRs are something quite logical and a lot of emphasis on other aspects of you that have nothing to do with looks
Extremely unlikely that you slept with her and the she told you “ you are a great guy but I can not have a relationship with you because you lack a couple of cm in height “
Most likely she liked you physically but she did not see a future with a guy like for various reasons
This height whining of guys with above average height is like a guy who has above average penis size and he is frustrated that he does not have it at least 20 cm ( like porn actors do ) and the reason on why girls do not want to sleep with him
If you go for girls that are maximum 1.65, 15-16cm is more than you can fit in without the girl feeling pain. So a bigger penis in this case is not really helpful
Maybe a 20cm penis for a 1.80’girl would make sense, but is not really needed