In this case just pull the line 1 cm. It's worse when you insert the UV line shortly after birth, and when the baby develops distension after a day or two, the tip will be pulled to the level below diaphragm. It happened to me several times. For that reason I try to place the tip rather at T8 then T9. If the tip gets pulled to the level below diaphragm on the AP XR, you may still be able to salvage the line by getting a cross table lateral XR which will show more precisely the position of the tip in relation to the posterior diaphragm, and if you are lucky it may be still positioned above it.