Sorry to hear you were sick. No problem, I check here everyday.
Okay, what height did you put on the padded FR envelope?
Now here is the thing, I see the padded FR is 12.5 x9.5 - height to be determined by you.
With your measurements, if you have at least a 2.5 height, that envelope is going to fit 15 jars.
What you need to do is adjust the measurements of your jars.
If you only want to fit 6 jars in that size envelope you need to figure from there.
If your measurements were 4x4x2.5 with an envelope height of 2.5 - only 6 would fit.
To get these figures I am. for your original size, adding how many 2.5 inches can go along the length of 12.5 inches which is 5.
Then I'm doing the same for along the width of 9.5 inches which would be 3.
So 3 rows of 5 = 15 jars.
If your length was 4 then only 3 would go lengthwise (3x4=12) and if your width was 4 then only 2 would go widthwise (2x4=8). As long as the height was no more than from 3 inches, then only 6 jars would fit.
I did not figure how that would effect your jars going into regional or flat rate boxes, but of course it would be less than with your original measurements.
I'm just trying to show you how you need to figure your dimensions against the mailer or box dimensions you have listed.
The calculator works on numbers. It does not know what you are selling or how things actually fit, it can only go by the dimensions you give it and the dimensions of the boxes you provide.
I hope that helps.