The model is doing its best with what you give it. These five habits consistently produce better reads.
Shoot from about 45 degrees
Straight down flattens everything and hides depth, which is exactly the signal used to estimate volume. A three-quarter angle keeps both the outline and the height of the food visible.
Get the whole plate in frame
Cropping tightly removes the plate rim, and the rim is one of the most useful size references available. A dinner plate is a known quantity; a close-up of lettuce is not.
Use daylight where you can
Warm indoor light shifts colour badly, and colour carries information about doneness, dressing and ingredient identity. Near a window beats overhead bulbs.
Separate what you can
If the sauce is on the side, photograph it on the side. Components that overlap are components the model has to guess at.
Scan before you start eating
Obvious, but it's the single biggest one. A half-eaten plate is a portion-estimation problem with no good answer.
Try it yourself
Point your camera at your next meal.