Hi GH,
Just my two cents...
When I had nuclear Gastroparesis testing, I sat up about a 30 degree angle and was given Oatmeal, since I do not like eggs. The whole test lasted about 2+ hours, with feedings and pictures taken at specific intervals. Even though I had a bit of reflux at that degee of recline, the test proved normal for me.
The radiologist was really great - she spoon fed me (certain amounts.) :)
The entire time for the test does depend if if have normal motility, hyper or hypo.
Once the last bit of food enters the Duodenum, the test is offically over.
FWIW,
GM