A soil test results that I ran thru my U. Ext. gave the following Mg interpretations:

SANDY SOIL
low medium 100 to 600
high >600

SILTY SOIL
low medium 200 to 1200
high >1200

(No numbers given for clay.)

These numbers are values reported in lbs/a which appears to be what your number is. You are in the medium range which should be adequate & if you decide to add any Epsom salts , I wouldn't use very much.

Good answer by wirosarian. It is important to know whether results are reported in pounds per acre or parts per million. The results page should say.

Some experts say the ratios between potassium, magnesium, and calcium are significant. Others say it doesn't matter as long as there is enough of each. In your other thread you reported that calcium is nearly 20x the magnesium (very high ratio) and that magnesium was only slightly higher than pootassium (fairly low ratio). With your extreme calcium levels, it's possible that more magnesium could help by creating a more normal ratio. On the other hand, magnesium levels considered on their own are OK, depending on the unit being reported, so it may not matter.

So that's why I said on the other thread that a moderate amount of ES wouldn't hurt in your case.

I think you should do a test. Divide your roses into two groups. Divide the punier roses equally between the groups. Write down the groupings. Give one group 2 TB epsom salt in a gallon of water and the other group just a gallon of water. Then compare the groups in a month and see if there's a difference, especially in new basal growth. If you put ES on all your roses, you'll never know, and you'll probably be dooming yourself to repeating the ES ritual forever.