Boron seems to be ok in any bone supplement because it effects hormones and how the body regulates magnesium, calcium etc.

The reason you don't take strontium with calcium is because you wish to have the body absorb strontium and the calcium receptor will choose the calcium over strontium so you will just be "peeing" away the strontium if you take it with calcium.
If you take strontium without calcium the calcium receptors seem to take strontium up and use it. Plus, there seems to be evidence of a receptor for strontium in bone, but that is just one study and there needs to be more research.

I and all the strontium users whom I know use strontium citrate. I use the AOR brand because it originates in Canada where they monitor supplements much better than the USA.

I believe that I sent you several links earlier for research about strontium. Strontium does not replace bone. It grows bone. See photo with research linking and see links below

Bone is made up mainly of collagen and calcium plus lots of various minerals including strontium, especially if you live where strontium is in the ground water, and you don't filter the strontium out.
Strontium is heavier than calcium so when you are using a calcium measurement like DXA the Dxa will read about 10% higher than if you just have calcium in your bones.
I know of several women who were fracturing who started strontium citrate and quit fracturing. Research says that strontium users are 47% less likely to fracture than the users who did not take strontium. see research links below

If you don't mind saying, what was your last dxa reading. Also have you cked your hormone levels to make sure you have the hormones which you need to grow bone.
Growing bone is a synergistic combination of many factors including exercise, supplements and hormones. Make sure all those are in the optimum zone before you add strontium. That advice is from someone who has taken strontium citrate for years, only take strontium after you have cked all other natural supplements, hormones, exercise. But I personally would take strontium citrate before I took Big Pharma Meds.

Still, everyone has to make their own decisions. Just be sure to do your research before you make any decisions.

Here are some links to Inspire postings about strontium
https://www.inspire.com/groups/national-osteoporosis-foundation/discussion/strontium-studies-and-research-articles/?origin=freshen
https://www.inspire.com/groups/national-osteoporosis-foundation/discussion/strontium-does-it-prevent-fractures-research-articles-personal-stories/
As always warmest wishes to you my friend.