Greetings Lexus owners! Have you ever measured your IS’s ride height and compared? I really wonder how much difference have you found? Do you think .40 inches is acceptable?

That seems a little excessive.
Where and how are you you measuring it?

I measured it from the fender lip to the wheel center.

Since there is a measurement at each wheel...what were the 4 measurements? So we can get an idea of where the vehicle is higher/lower than the other measurements.
Also are you measuring it somewhere level...realistically it's hard to find anywhere that's truly level, but on concrete shouldn't be that bad...asphalt is just a disaster.

So true. Even on concrete what I thought was level I got bad results. Brought it to my suspension place positive i had an issue, they measured with the car between their lift posts on concrete and car was even.

Cars don't have to necessarily be even. For example BMW's are famously always lower on one corner, (I believe right rear) to compensate for driver weight and other factors. This did bother me so what some owners, including myself did, was ordered up one BMW OE AWD spring pad which would raise up the RR wheel just enough to make the car even all the way around. Even though this would technically throw off the recipe BMW so carefully baked into the car, for my purposes, it allieviated my OCD. lol. But yeah just drive the car and enjoy it. Unless your car is 200 years old or it got plowed into the back by a fully loaded ford expedition, there's almost zero chance there's something wonky with your car because it sits a tad lower (or higher) on one of the wheels.

As I did the measurements results changed drastically. Initially left rear and right front were low to the ground. Today I couldn’t find somewhere level enough, but had the following numbers picking the datum 375mm:
(LR, RR, LF, RF respectively)
+1, -2, 0, +3

Thanks a lot for the great advices.