I'm another one with retinal toxicity after being on 400mg daily for 12 years. I am short, 5 ft3/4 inch and weighing roughly 52 Kg /115 pounds or slightly less at times. I started taking it in 2000 and quit taking it in 2012
I researched the drug at the time it was first prescribed and I didn't find any dose recommendation according to weight suggestions.

First dosage to weight suggestion occurred in 2002

Then in 2011 they made changes to those weight to dose suggestions.

At that time they said a maximum dose of 400mg per day was safe unless a person was short .
For a short person 6.5mg /Kg based on ideal weight, not actual weight was to be used .
They said if a person was very thin/ underweight, calculated on actual weight resulted in too large a dose
I was not underweight, so dosing at the ideal weigh happened to be what I weighed and I should have been taking a maxium dose of 323 mg per day.

And then in 2016 their were new suggestion again this time using real weight was under 5mg/Kg.

It is the cumulative dose that gets you into the danger zone. The cumulative dose of plaquenil is not stored in fatty tissue ,only lean tissue. And so whether a person is overweight or normal weight also effects how fast the cumulative doses get you into the danger zone.