The "over the counter" form of Vitamin D (cholecalciferol) needs to be converted to calcifediol (25OHD3) which is the form doctors normally measure (which you seem to be ok with your levels), and then converted to the active form calcitriol (1,25-dihydroxyvitamin D3) that uses the VDR for some of Vitamin Ds functions (but not all). Your doctor is able to test the active calcitriol 1,25-dihydroxyvitamin D3 (the active form) at the exact same time that they test calcifediol (25OHD3) as usual by the way to see any issues in conversion at the time of the test.
https://www.labcorp.com/tests/081091/calcitriol-1-25-di-oh-vitamin-d and
https://www.labcorp.com/tests/081950/vitamin-d-25-hydroxy
https://pubmed.ncbi.nlm.nih.gov/29713796/
Your doctor can also prescribe calcitriol 1,25-dihydroxyvitamin D3 the active form which may be more helpful during active shingles infection for example according to that research since the conversions can be problematic during that time. Zinc and Vitamin A are also needed for the Vitamin D receptor to function properly and those can also be lowered during chronic inflammation/infection so if even the 1,25 form isnt working great by itself in those special cases, those nutrients I'm mentioning can be potentially added as well temporarily which is also new information.
See here, let me know if you still have a question.
https://www.healthline.com/nutrition/vitamin-d2-vs-d3#TOC_TITLE_HDR_2
According to the latest research, around 30ng/ml seems to be more of the optimal level for some people, with 20-30 being normal while its looking like there are differences among the population with those who have VDR mutations, get negative effects from D unrelated to turning on immune system, or are blood type A, its possible that your genetics actually favor a much lower level of vitamin D naturally unless you are currently under a severe infection/inflammation/covid state and at least for me, and perhaps all blood type A's as I'm finding just handle inflammation differently which is why we have all those mutations in inflammation pathways and MTHFR mutations etc, and is why I dont always discuss what works for me as it may differ a bit for others. We are all unique...just like everybody else.
Vitamin D is converted to active form and utilized when you also take magnesium, and helps keep your levels optimal around 30 ng/ml. Magnesium does not continue to raise Vitamin D levels over 30ng/ml but brings them back down when higher back to around that level. Magnesium was found to have a regulating effect, raising and lowering vitamin D levels based on the original starting baseline 25(OH)D levels. In those people who had a baseline 25-D level of 30 ng/ml or below, magnesium supplementation raised up their 25-D level as expected. However, In those who started out with higher 25-D baseline levels starting around 30 ng/ml (75 nmol/L) up to 50 ng/ml (125 nmol/L), magnesium supplementation LOWERED THEIR 25-D levels back down, not raised 25-D levels to even higher levels that some suggest is an optimal level (it appears its not according to many new research findings that needs to be reconsidered). Magnesium regulates vitamin D levels, low magnesium impedes your body's ability to utilize vitamin D, even when it's present or taken by supplementation. Magnesium deficiency shuts down the vitamin D synthesis and metabolism pathways.
https://academic.oup.com/ajcn/article/108/6/1249/5239886