With my lower back pain a thing of the past I remain mindful of my lower back and pelvis region.
However, recently I have received two opposing points of view on pelvis positioning.
Always keep the pelvis actively tucked in/ under
‘Pelvis tucked in is old fashioned advice’ and it is healthier to maintain a natural curve in the spine i.e. pelvis not entirely tucked in
Which is it? 
For me it is neither. I have not used the term “tuck the tailbone” for ten years. I have found this instruction (again, for me) to be an instruction of last resort and therefore only use it when I am flummoxed and cannot otherwise “reach” the student with other directions.
We live in a society where we are often guided/led only by pelvic or vital force AND most have a leaky force at that. Such leadership inhibits our ability to mindfully evolve as the force being referenced is the force of survival, procreation, desire, lust, and craving. It is not a “bad” force it simply blocks aspiration (movement upward toward the heart center) when it is out of balance and therefore dominant.
With that in mind, it is helpful for those on the path of evolving mindfully or aspiring, in the yogic context, to contain the pelvic force, lift it to the heart and work to transform it. Such an action should be maintained but should not sacrifice healthy curvature in the lumbar spine. In fact said curvature is not sacrificed when the aspirational action comes from the pubis upward rather than ONLY a drooping from the lumbo-sacral region downward.
So for me it is lifting the bottom of the belly (which lengthens the spine) rather than tucking the tailbone which tends to compress it, harden the buttocks, and strain the low back. It is important to note that each student may be structurally “different” and need unique instructions which are almost always contradictory but complementary. And it is for this reason that I suggest OPs seek a teacher, not because I enjoy saying it.
Thanks for the insight IA.
What is interesting is that when I had lower back pain my root chakra was green which is the colour of the heart chakra, not sure if this carries any significance to what you refer to as the ‘pelvic force’.
My back pain has stopped but I don’t believe it was from any physical treatment, I think it might have had something to do with my inner being at the point when I felt the pain…which could have been my ‘leaky force’, but I am not sure exactly which forces were at play.
I’ve heard it the IYT gathering, that practicing muladandha helps with lower back problems