The syringe you're talking about would probably work great and is what's ideal. I've seen those before, but for me, I was just messing around yesterday with things I had lying around for the exact same reason (my kits are coming today...woo-hoo!😗). Besides the fact that I had the tapered syringes already (to administer medicine/food to my pets), I also just think they may be better/more versatile. Like you said, and what I've noticed when playing around with my perfumes, the atomizer spray thing underneath the cap can vary in size. Using a tapered syringe ensures that you can have a tight fit because you can always cut a little bit off until it's snug. That's also very important...I learned my lesson yesterday when I spilled perfume on my carpet because the nozzle/tip of the syringe wasn't fitted to the atomizer piece. Another thing, when/if you've successfully got perfume in the syringe, flip your syringe upside-down so that perfume doesn't leak out the tip.
I used 40.6 g of decent flower, 6 g of kief, and about 500mg of distillate from an old cart. The flower and kief were decarbed at 240deg Fahrenheit for 40 minutes covered in foil. I used 12 ounces of high quality MCT oil and 1 tablespoon of sunflower lecithin, then added everything to a crockpot on low for 4 hours stirring every 30 minutes or so. Each cap should be roughly 23mg of THC.
edit for links of everything I used https://www.amazon.com/gp/product/B01LYCIHL1/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1 (empty capsules used, they have been great so far) https://www.amazon.com/gp/product/B0781D9QYX/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1 (capsule filler that I literally only use to hold the capsules, would not buy again) https://www.amazon.com/gp/product/B078K8SVMN/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1 (syringes used to fill the caps)
Try a manual water syringe. Seems to work the best for me. People say waterpik, but I honestly don’t know how they do that, there isn’t enough control and they seriously hurt my tonsils.
With the manual water syringe, you have to gently insert into crypts and apply water pressure, be careful not to hurt yourself.
https://www.amazon.com/TecUnite-Disposable-Measurement-Irrigation-Mouthwash/dp/B078K8SVMN/