As someone who frequently makes contact prints from paper negatives, I can attest that you can certainly get a decent exposure through the backside of print paper.
In the case of contact printing a paper negative, the light travels through the back of the negative, through the negative emulsion, then onto the face-up print emulsion underneath.
In the case of the OP's issue, he most likely exposed the projected image through the backside of the print paper, due to the paper being face-down on the easel.
I will offer another data point: I have also ENLARGED paper negatives, placing them emulsion side down in the enlarger negative carrier and projecting them onto the easel. This works better with a condenser enlarger and RC negatives, and higher contrast filtration.
Reading this and other posts by the same OP, he most likely is having issues with basic paper handling skills.