It sounds like you are taking calcium that comes in 600 mg per pill.

In an effort to figure out how I could make my body absorb more calcium, I did a little searching and stumbled upon info which states, “The body can absorb a 500-mg dose of calcium very efficiently — whether from diet or supplements. But as the dose increases above that level, absorption efficiency declines.”
https://www.health.harvard.edu/newsletter_article/By_the_way_doctor_How_long_does_calcium_absorption_take
I switched from 600 mg calcium pills to Citracal Petites, each pill had 200 mg of calcium, and I try to space my calcium from food and supplements throughout the day. My thought is, if my body always has enough calcium from my diet, my parathyroid glands won’t need to release PTH to “find” calcium and potentially take it from my bones to keep my blood calcium levels in range because my diet/supplements will be doing all the work. Also, calcium is the last thing I take before going to bed because this can potentially reduce resorptions markers during the fasting state.
https://www.nps.org.au/australian-prescriber/articles/bone-turnover-markers