Cart acts like it won't recognize the dimensions of products

I am Using USPS plugin, for priority regional & flat rate, am a newbie and appreciate any claririty.
1) Will I need to enter box dimensions for Priority Flat Rate option? It’s enabled but doesn’t show in cart as option, regional does.

The USPS plugin says “Note: If you are using regional rates, A1, A2, B1, B2 and C box sizes will be defined for you.”
2) So I assume this means USPS takes care of regional box sizes I don’t have to enter?

I have a group of same product in 3 different bottle weights & dimensions
16oz, 8oz, 2oz bottles.

cart adds product cost of 16oz bottle (25.00) or any bottle cost from drop down menu A-OK, but shows shipping for an “A” box ($5.35) for any item selected.

Strange–This $5.35 ship fee, seems similar to a priority flat rate “A” box fee (which is enabled), and cart only shows priority regional mail option in cart.

A 16 or 8oz bottle will not fit into the “A” box size. It must be a medium box due to size of bottles. (FYI qty 4-2 oz bottles will fit in the “A” box.)

I can add 5- 16oz bottles to cart (approx 10/lbs), & the product cost increases relative, shipping does not change until I add 6 bottles (12/lbs), and only increases to $6.16 for ship fee. This is still an “A” box all day long.

After reviewing website further, it acts like NONE of bottle dimensions are recognized, but increases cost at 10/lbs, and only to $6.16 ship fee.

It seems the cart isn’t allowing the 16oz bottle weight/dimensions to be used per the items chosen in this example, nor the regional weight, as it’s configure by weight, not $5.35 up to 10/lbs.

Cart allows qty 36-2oz bottles before price increses to $6.16 (10.35/lbs). No way will these qty of bottles fit in an “A: box.
So 10/lbs is a factor it seems for som reason.

I’ve added product weights by oz’s in product page, and variables. (I don’t know if attributes are required here, or their purpose, only added variables, please advise.)

Instead of grouping the bottles under one product, should I have a separate products listed on product page for the 16oz, the 8oz, and the 2oz?
3.) (The 2oz has different options although same weight/dimensions, nasal sprayer, eye dropper, finger sprayer, and assume these would be variables?).

Thanks
I’ve watched the tutotrials and they don’t give examples of the actions, after the product is entered, what it does and can’t see what it’s supposed to do in a real world scenario. This would really help us if videos did show the results of the actions to comprehend it better.

https://www.ads-software.com/plugins/woocommerce/