I know what you mean about it being diffucult to pull, I tend to add 100mls at a time, pull it as best I can but what I do is pull it into a jar that I know will contain some bark and lye but attempt to keep it to a minimum. I'll then let that settle out and then seperate the white spirit into another jar to ensure as little lye water is included. Repeat this 3-4 times and pool all into one or two jars and freeze precipitate. I take it you are doing Noman Tek? I don't think you get the best yield on this tek overall because it's messy and labourious, the next time I need to extract I'm going to try Q21Q21's lime tek, seems incredible easy and straight forward, you should check it out.
I'm thinking with a single 300ml pull you might not have got all that the bark has to offer - try doing a 100ml pull on the bark that is left doing it the way I described above, if you get good crystal fall out on that it may be a good indication that the 300ml pull didnt grab the majority of the good stuff and repeating 100ml pulls could pay off.
Methtical