just a suggestion - it may be easier for you to use the usual meaning of sf, that way you'll know exactly by how much did you sf your soap (and it will be easier for you to compare your results with those of others, rather than having your own way of defining things). the percentages are tricky thing, and it doesn't go the same way around adding 6% of oils or sf at 5% lye discount (well, i didn't calculate, it could be that this exact numbers hold true, but it's not a general scenario).
when you use the lye discount method, you measure all of your oils, and just subtract the one that you want to add at trace. say your recipe calls for some number of oils and for example 5 oz of almond oil. you just mix everything, except almond that you add later, when you reach the trace.
another thing to consider is smth i found out on this forum - at the time of trace about only 15% of your oils have saponified, so it does not do much difference when do you add your sf oil, nor which one it is..