You haven't created that impression.
The Catholic position is that not only is sodomy an abomination according to positive and specific revelation (i.e. the Scriptures), but that even those who have not been gifted with the grace of revelation can deduce the evil of sodomy by applying right reason and analyzing the evidence of creation.
The Reformed position (as I understand it) is that we only know sodomy as an abomination according to positive and specific revelation (again through the Scriptures) because man's reason, distorted by the depravity of sin, cannot arrive at a sure knowledge of God's truth in this matter through his defective reason alone. What we can do is, being vouchsafed the truth through Scripture, deduce from it the natural reasons for God's ordinance.
I think you understanding is mistaken. We divide revelation under two specific headings: General Revelation and Special Revelation. General Revelation are those things which we ~inferentially~ know to be true. I think most Reformed theologians would classify sex between a man and a women to be a general revelation to all men as the only role for sex regardless of any knowledge of special revelation.