(I can't link these directly from the database I'm using as its university access only but here are the references)
No difference in neural activity between homosexual and heterosexual males during erotic stimulation (in this case being shown pornography).
Kagerer, S., et al., 2011, "Neural activation toward erotic stimuli in homosexual and heterosexual males," Journal of Sexual Medicine, Vol. 8, 11.
Difference in Grey-Matter regions in homosexual->heterosexual women, but no difference in homosexual->heterosexual men.
Ponsenti, J., et al., 2009, "Brain structure and sexual orientation," Sexuologie, Vol. 16, 3-4.
Lesbian women differ to heterosexual males and females, however the difference is not significant.
Rahman, Q., et al., 2008, "A comparative analysis of functional cerebral asymmetry in lesbian women, heterosexual women, and heterosexual men," Archives of Sexual Behaviour, Vol. 37, 4.
Why do they have such cringey journal names :(
Whilst these don't mean that your studies are incorrect, it does raise the issue of significance and whether findings with such small sample sizes could be down to chance, or due to an element of the selection procedure. For example perhaps if only very effeminate gay men came forward, and only very butch heterosexuals also, then the difference would be much more profound than an average comparison. With such small numbers such as 20 and less it's highly possible.