Encourage A4 to page break before a tune. This enourages page breaks to happen before tune start, and not between the tune image and any following wording. Also move the vfill to the tune start. That way, if the break does not happen, the vfill will, and the following tune will be spaced down to the bottom of the page if it's the only other tune on the page. Otherwise everything tends to clump at the top of the page.

X: 1
T: Albert Farmer's Bonfire Tune
M: 4/4
L: 1/8
K: D
Q: 160
de | \
"D" f3d  A2F2 | "A" G2GF G4  | edcA B2c2 | "D" dffd A2de |
"D" f3d  A2F2 | "Em" G2GF G4  | "A" edcA B2c2 | "D" d6  :|
de | \
"D" f2fd f2f2 | "A" gf "D" ed "A" c4 | gfed cABc | "D" dffd A2de |
"D" f3d  A2F2 | "Em" G2GF G4  | "A" edcA B2c2 | "D" d6  :|