Hi Kelly!
Welcome to the board :) Ahhhhh, it sounds like you are about to become candlemaking obsessed :) We will probably see you around here a lot ;)

A candle is made up of wax, wick, scent, dye and other additives. Each componet will affect how a candle burns. So even if you make the exact same size candle with the exact same color, dyes, additives and wick adding different FO's will cause your candle to burn differently. It also may depend on the temp that you pour your wax. If that changes each time that you pour then your candle will burn differently. There are many different outcomes and that is why it is really important to testburn EVERY type of candle you do :)

The most common burning problem from using different FO's. For instance Vanilla's are generally more dense (heavy) then most other scents so it needs a bigger wick.

Also, some scent/wax combos just like different families of wick (CD, HTP, square braid, etc)

When you make a candle you will want to write down EVERYTHING that you do because you simply won't remember it and if your candle works well then you will want to repeat it!

I would start with observing which FO's cause your candle to tunnel and upping the wick on them and seeing if they burn better.

Testing is really important. You don't ever want to give someone an unsafe product! Everyone has different ways of testing and this is the way that I have found to work the best for me to really know my candles

I have tested a ton of candles and I know how to read my wax and scents pretty well at this point. The way that I test votives is different from how I test containers. For votives I start with 8 of the exact same ones. I use CD4 in half of them and CD5 in the other half.

I take their initial weight, temp originally poured, room temp poured at, color used and amount, amount of FO used, supplier and name of FO, additive changes (if any) . Each 1/2 hour I look at the flame height, melt pool (height and depth) and I take the weight. For a votive the MP should be all of the way across in about 2 hours. If it is faster then that it will end up sooting and if it is slower then that it probably won't get hot enough to give the ultimate scent throw.

You should also burn your candle all of the way down because your candle may burn differently at different times.

The reason I test so many votives at the same time (and side by side) is that the more that you have the more certain you can be that you are getting the correct results. There are so many times when I have tested just one votive and for some reason it gives weird results. This way I am able to instil a lot of confidence in my results :)

This is certainly not all inclusive. I could write forever. :) Just let us know if you have any questions :D

Now, if you have any specifics that you need help with just let us know what wick, wax, FO and addives that you are using along with amounts. We can be a lot more help like that :)