I digged further into this spray. Apparently its intended usage is use it on clothes before you put it on. Not using it while wearing the clothes (now you're spreading alcohol on your body, not very safe)
After some try and error, I think 4.8 g L-Menthol disolved into 60mL of 95% ethanol, then diluted with 40mL of water is a acceptabled recipe. I feel no different with the original one. You may use 5g L-Menthol if you think it's not strong enough. For coating the cloth with menthol (so you can feel cool when you start sweating), I think you can use less ethanol as long as the menthol don't precipitate out.
If you intent to use directly on your skin, you may lower the amout of menthol and add a bit more ethanol. Too much menthol feels like buring (your skin think it's too cold), and the evaprate of ethanol will actually cool your skin.
However, I do want to mention that you should not solely rely on this spray to cool your body. Only the alcohol is cooling your body physically. The menthol is tricking your skin to think it's cold, but actually not.
I don't know if this will trick your brain to stop sweating and eventually lead to a heat stroke. So please use with care.
I always keep a fan blowing air to me when using this spray. To ensure I won't overheat.
Fun fact: Since all my ingredients are food grade, and I saw some paper said you can apply menthol internally, I did try drink some of the product. There are around 10mL of spray and I pour it into 300mL of drinking water, and taste a bite.
HOLY SH*T it taste really bad my mouth feels burning and it's not pleasure to drink.
Also, I don't feel too much internal cooling. I do feel some, but it's not strong. I would say just drink some ice cold water. Do not drink this.