Always good to wake up....
Sorry - I realise it sounds pedantic - it's simply that on my lipid panel; this ratio is explicitly stated - "Serum Cholesterol / HDL ratio: 4.2"
In your post, you had not listed it, though clearly, it's not a difficult piece of mathematical gymnastics to figure out the number.
The reason why there is a difference - is that - I believe both ratios to have important meaning, but I would struggle to persuade a diabetic nurse to pay any attention to my Trig/HDL ratio when my LDL level is higher than the threshold.
However - if a number is explicitly stated on the lipid panel result - that means that someone operating within the professional guidelines also believes that is an important number, so at least I have a way of making a positive argument "look, you know that I'm on a very low-carb diet, and there is some research that suggests that people like me may have elevated LDL, but the deeper research suggests that this isn't necessarily a risk if your total/HDL is within 4.5 - which mine is.. so can we just agree that it's all good?"