Hi Roland,
When our sport (or passion) was beginning many people thought that the lung volume will limit the depth, there was a rule that the athmospheres that our body tolerate was TLC/RV (TLC=Total Lung Capacity and RV=Residual Volume).
Bob Croft has a huge TLC and many explained his depths because the TLC/RV relationship was still high, but after him many others like Majorca show that the theory was wrong.
If we take in account just the air in the lungs the depth limit for many of us will be around 40 meters. The blood-shift just change the air content of the thorax with a fluid (blood) making the thorax less compressible. In the Craig chapter of Diving limits of the Book "The Physiology of Breath-hold Diving" he describes experiments with inmersions starting at RV, and the transthoracic pressure weren't as high as it should be, thats how the concept of blood-shift was born.
As you are going down, your lungs will compress but the thoracic cage is more rigid, so it doesn't compress as much as the lungs, that make that intrapleural pressure goes more negative and also the transpulmonary pressure.
With a "negative" thorax and due to the effects of inmersion there is a blood flow redistribution toward the thorax, and the lungs become less compressible thats why the humans can withstand that incredible depths.
As our organism is not static, I think that with training is possible that our pulmonary vessels "learn" to support higher pressures.
My advice:
Don't worry about your RV, it doesn't really matters.
The blood-shift will come, some feel like a sharp pain in the thorax at certain depths, and that will indicate a huge lung compression, but it doesn't mean a blood-shift.
If you are training CW diving you will have the blood-shift, also you can try negative diving to improve your ability before you go to the sea.
Don't hurry to reach extreme depths, do it at your own pace.
When I started serious freediving I felt that chest discomfort at 35 meters, and thought that it was my depth limit, then it moves to 38 and 2 weeks ago I made 40 without any discomfort.
For deeper dives you can warm up with shallow dives in exhalation to make the blood-shift maximal before the deep dive.
Remember this is fun, go next week to the ocean without fears and do what your body tells you, it won't go wrong.
Hope to helped you