OK ... just wanted to see if you were adding the EO before the cook. I talked with someone this summer who thought it was strange that I added them AFTER the cook. I mix my EOs with my superfat oil(s) and it's the last thing that goes in.
After my bars are cut, I set them out to 'dry' on wire racks for no more than 2 weeks. (I also use natural colors, and the longer they're out in the light, the quicker they fade. Many colors fade faster than the scent.) Then they get placed in plastic shoe boxes with 2 layers of tissue paper between each layer of soap, and the lid popped on to finish their cure. I wrap my salt soaps individually in quality paper napkins (otherwise they can make a mess when they 'sweat'), then box them as the others. These cheap plastic shoe boxes are not air tight like plastic food containers, and they seem to store well this way for me. I've been doing it this way for years. Each scent goes in it's own box, so there's no 'muddying' of scents.
The scent shouldn't dissipate any faster just because you're using single oils. You mention you don't mix any EOs because you don't want to 'muddy' the fragrance. True, if you're going for a particular single note. On the other hand, mixing 2 essential oils in equal amounts often gives you something new with more depth. I'd encourage you to try it! When it comes to using several EOs in a blend, though, it can take years of blending before you get to the point you're getting 'nice' blends consistently. Kind of like cooking 'off the cuff'.
My favorite suppliers for EOs are:
1) New Directions ... good oils, good prices (sometimes REALLY good prices), reasonable shipping
2) Liberty Naturals ... awesome oils, good prices, their shipping SUCKS!!!! Which is the ONLY reason I don't order from them more often or why they're not #1 on my list! They will NOT give you a total, including the shipping costs, when you order. They decide AFTER they package your stuff up how much they're going to charge you for shipping. One year I placed an order with both ND and LN at the same time. When the orders came in, I had twice the amount of products from ND in a smaller box than LN had used! And of course, the larger the box, the more shipping costs. Very frustrating!
3) Camden Grey ... good oils, good prices on some oils, reasonable shipping ... BUT they are NOT a 'friendly' company, or so I've heard. If you never have an issue with them (I haven't), they're just fine. After reading all the horror stories about them, I check, double check, triple check, my orders before finalizing them. Then again, that's what I do anywhere I place an order. lol
I've used all 3 companies for years ... Liberty Naturals I've been using the longest, 20+ yrs.
Don't know what kind of EOs you're using, but theoretically, that could be part of your problem. If you're buying them from, say, eBay, there's lots of disreputable sellers on there that claim their EOs are pure. Sure, they're pure, but diluted, and they don't tell you that part. Just throwing that out there!