It’s worth remembering that you are dealing with two models here, both of which may not be great at representing your physiology:
(1) The Critical Power / W’ model from which you have got some values that represent your current fitness level. You haven’t stated how you determined your FTP, but you have said you have determined your W’ from just one effort - this may not be the best way to determine your W’. There is quite a lot of academic literature out there looking at how an individual’s CP / W’ can vary significantly by choice of defining tests. If you want a read, here is one, admittedly quite long!
(2) The W’ reconstitution model, which has been discussed in a number of threads (here’s one) and is not tuned to your actual recovery abilities which likely differ to the standard assumptions.
As for what to do with that information, for me it depends on what you want to use W’ (balance) for. If it is just for tracking your fitness / performance over time, and if you are testing in a consistent manner, I don’t think it matters if you see significant variance from W’=0 when you are actually completely spent from above threshold work. If you want to use it to help gauge how much you should have left in the tank as during particular types of rides, you may want to look at different protocols for determining W’ (and CP). That could be different tests (duration, quantity, etc), doing your 6 minute effort after you have already done a certain amount of work, or something else.