I'm no expert by any means as I've only just started DIY but I read someone's recommendations to try mixing various manufacturers' same flavors as a good way to bring out various taste nuances from that flavor. I've also used a recipe for Strawberry Shortcake Bar that lists just Strawberry but under which are comments from folks suggesting mixing it with Ripe Strawberry for a more full taste. So I'd suggest you try and experiment with them.
Based on the recipes I've seen I'd suggest starting with a total of 8% strawberry and if that dosen't seem enough then try 10%. The mix depends on what you like so mix up 5-10 ml of each and try them out to decide on what ratio of each would make up the 8% to 10%. Also be aware that the taste of the strawberry in your
juice will change over steeping time so don't decide too quickly. On that recipe I mentioned above I went with 50/50 to make up the total of 8%.